Biaxially stretched polyamide resin film

ABSTRACT

Disclosed is a polyamide resin film which has excellent dimensional stability with respect to moisture absorption, excellent mechanical characteristics and sliding properties under high temperature and high humidity conditions, and excellent handling properties. Specifically disclosed is a biaxially stretched polyamide resin film, to which 0.3-10% by weight of an inorganic material including a layered compound is added. The biaxially stretched polyamide resin film is characterized in that the layered compound is in-plane oriented, and that the film has a haze of 1.0-20%, an elastic modulus in the longitudinal direction of 1.7-3.5 GPa at a relative humidity (RH) of 35%, a surface roughness (Sa) of 0.01-0.1 μm, and a coefficient of static friction (F/B) of 0.3-1.0 at a normal stress of 0.5 N/cm 2 .

TECHNICAL FIELD

The first invention relates to a film of a resin containing a layeredcompound commonly called as a nano-composite. More particularly, theinvention relates to a stretched film of a nano-composite polyamideresin of which stretching at a high ratio has conventionally been saidto be impossible with an addition amount of 1% or more of the layeredcompound.

A conventional nylon film is made slidable by roughening the surface inthe case the slipping property is needed under high humidity, since theslipping property is changed in accordance with humidity. However, inthe case of a film containing an inorganic layered compound, thealteration of the slipping property relative to humidity is small. Inaddition, even if the surface roughness is small, a sufficient slippingproperty can be exhibited and therefore contradictory characteristicssuch as gloss can be satisfied simultaneously.

The second invention relates to a biaxially stretched multilayerpolyamide resin film laminated with an olefin resin film such aspolyethylene, polypropylene, or the like. The resulting multilayer filmis preferably used for wrapping retort food products, since the laminatefilm is tough and has excellent pinhole resistance. More particularly,the invention relates to a biaxially stretched multilayer polyamideresin film with little boiling strain in the entire width of a film rollin the case of using the resin film as a wrapping material.

The shrinkage stress of a biaxially stretched polyamide resin film canbe lowered by providing the above-mentioned multilayer structure to thesecond invention and as a result, strain caused by bowing at the time ofboiling can be suppressed. Further, in the case a layered compound issimultaneously added, the gas barrier property can be improved and theboiling strain can be concurrently lessened.

BACKGROUND OF THE INVENTION

A biaxially stretched polyamide resin film is excellent in themechanical characteristics, barrier property, pinhole resistance,transparency, etc. and has been used widely as a wrapping material.However, due to a high hygroscopic property derived from amide bonds inthe polymer structure, the mechanical strength can fluctuate, andhygroscopic elongation occurs in accordance with fluctuation in humidityand besides, problems tend to occur in many kinds of steps. Furthermore,the glass transition temperature of the resin itself is not so high andimprovement of heat resistance, particularly, the mechanical propertiesat a high temperature, has been desired.

Moreover, a common polyamide film made of nylon 6 has a high elasticmodulus but low elongation, and accordingly shows a lowered maximumpoint stress and rather brittle characteristics in a low humidity. Onthe other hand, the polyamide film has a low elastic modulus but highelongation, and accordingly shows an increased maximum point stress andductility in a high humidity. When modifying the stretching conditionsfor improving the characteristics in lower humidity, there occurs aproblem that the film characteristics are unbalanced. As described, acommon polyamide film shows considerably changed characteristics inaccordance with the humidity level as compared with a film comprising apoly(ethylene terephthalate). Therefore, it is necessary to control thehumidity in the film production process and to determine the processingconditions on the basis of previous estimation of characteristicfluctuation.

Further, a biaxially stretched polyamide resin film shows a decrease ofthe mechanical strength and hygroscopic elongation due to the highhygroscopic property derived from amide bonds in the polymer structure.In addition, the difference of shrinkage quantities at the time ofboiling the polyamide film tends to cause problems in many steps due tostrains and curls formed in the film.

The strains at the time of humidity absorption and boiling are generateddue to relaxation of the structure at the time of stretching. When amaterial with a high stretching stress is stretched, the shrinkagestress generated at the time of relaxation becomes high and the strainalso becomes significant. Therefore, it is supposed to be possible thatthe strain or the like can be suppressed by lowering the shrinkagestress; however in the case of a polyamide resin, it becomes difficultto change the stretching stress due to the strong hydrogen bonds betweenmolecules and thus it is difficult to lower the stretching stress. Someof previous documents disclose decrease of boiling strains; howeverthere is no technique disclosed for lowering the stress (Reference toPatent Documents 1 to 3).

-   Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No.    2006-96801-   Patent Document 2: JP-A No. 2006-88690-   Patent Document 3: JP-A No. 2007-237640

As described above, with respect to a polyamide resin film with loweredboiling strains, there is no investigation on lowering the boilingstrains, while paying attention to the stretching stress.

Further, it has been known as a method for improving heat resistance andthe hygroscopic property of a polyamide resin that a layered silicatecan be evenly dispersed. This technique has been known well asnano-composite formation. Since the above-mentioned variouscharacteristics can be improved by the nano-composite formation, it isexpected that a film with improved characteristics can be obtained byfilm formation. However, in reality, the resin is generally poor in thestretching property and unsuitable as a resin for stretched films.Particularly, it is said that in order to sufficiently improve themechanical properties, addition of 1% or more of a layered silicate tothe polyamide resin is needed; however the stretching of a polyamideresin with a high layered silicate content is considerably difficult.

Patent Document 4 discloses a biaxially stretched polyamide filmcontaining a layered silicate. The highest reaching temperature for thesuccessive stretching in the width direction followed by thelongitudinal direction for overcoming the difficulty of stretching is ashigh as 180 to 200° C. Not only difficulty of production, but alsodifficulty of crystallization, is promoted too far before sufficientstretching in the width direction is performed. As a result, there occurproblems such that the layered silicate cannot be sufficiently oriented,various effects due to the addition of the layered silicate are notexhibited, thickness unevenness occurs in fine regions, and pinholeresistance cannot be satisfied.

-   Patent Document 4: JP-A No. 2003-20349

Further, as being understood from the scopes of claims of the specifiedmethods described above, practically the amount of a layered compound is1 wt. % or lower (including the organic matter contained in theinterlayer). If the amount of layered compound exceeds 1 wt. %,whitening at the time of stretching and poor productivity at the time ofhigh stretching ratio occur. These drawbacks are supposedly attributedto that the stress that tends to be converged on the tip end of thelayered compound at the time of stretching such that creases and cracksare easily caused.

Further, Patent Document 5 discloses a stretched film in a systemcontaining 0.5 to 5% of a layered inorganic compound but does notdescribe any concrete countermeasure for solving the above-mentionedpoor stretching property nor discloses any technique for a stretchingmethod with industrial productivity by successive biaxial stretching ina system containing a layered compound in a high concentration of 1% orhigher and consequently, results in investigation in a level ofsimultaneous biaxial stretching of small specimens in a laboratory.Also, there is a description in the specification that a layeredinorganic compound such as montmorillonite has an effect on improvementof the slipping property due to decreasing water absorption. However, anequilibrium moisture content of a resin is increased if a material suchas montmorillonite is added to a nylon resin. Based on this, it can besaid that the essence of the invention is significantly attributed tothe effect of the addition of the inorganic lubricant.

-   Patent Document 5: JP-A 2003-313322

On the other hand, Nishino et al, Kobe University pointed out aninteresting result with respect to evaluation of the orientation of alayered inorganic compound dispersed in a stretched film (e.g.,Non-patent Document 1). In this report, they paid attention to 060reflection in a layer of montmorillonite and reported that thereflection intensity was increased in the meridian direction by in-planeorienting montmorillonite.

-   Non-Patent Document 1: Molecular Nanotechnology 174^(th) Conference,    first Seminar, Preprints, p 22-23, Jul. 13, 2007

Further, with respect to piercing strength, this characteristic can beexhibited by increasing the in-plane orientation of a polyamide resin.If a layered compound is added to further heighten the piercingstrength, contrarily the stretching ratio cannot be increased, and thusthere is a problem that the piercing strength is scarcely improved ascompared with a film containing no layered inorganic compound.

As described, in the extension of conventional techniques, theindustrial production of stretched films of polyamide resin havingexcellent mechanical properties has been difficult.

Also, generally, for providing the slipping property to films, particlesare added as a lubricant to form projections on the surfaces. However,in the case of a polyamide film, since the resin becomes soft and theslipping property is lowered due to an increase in humidity, it isrequired to roughen the surface for achieving the desired slippingproperty even under high humidity. Therefore, there occurs a problem ofworsening the gloss in a polyamide film having improved slippingproperty under high humidity.

BRIEF SUMMARY OF THE INVENTION

The invention provides a biaxially stretched polyamide resin filmcontaining 0.3 to 10 wt. % of an inorganic material including an layeredcompound, wherein the layered compound is in-plane oriented and the filmhas a haze of 1.0 to 20%, an elastic modulus in the longitudinaldirection of 1.7 to 3.5 GPa at a relative humidity of 35% RH, a surfaceroughness (Sa) of 0.01 to 0.1 μm, and a static friction coefficient(F/B) of 0.3 to 1.0 at a normal stress of 0.5 N/cm².

The invention also provides a biaxially stretched multilayer polyamideresin film having 8 or more layers in total and using a same resincomposition for 80% based on the ratio of the number of the layers,wherein the film is stretched 2.5 to 5.0 times in the longitudinaldirection of the film and has an in-plane orientation coefficient (ΔP)of 0.057 to 0.07 and a strain of 0.1 to 2.0% after boiling treatment.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is an X-ray diffraction intensity plot of Example 8.

DETAILED DESCRIPTION OF THE INVENTION Problems to be Solved by theInvention

The first invention aims to provide a polyamide resin film excellent indimensional stability with respect to moisture absorption, mechanicalcharacteristics and a slipping property under high humidity and hightemperature, and a handling property. The film is prepared by stretchinga polyamide resin in which a layered compound represented by a layeredsilicate is evenly dispersed and which is conventionally difficult to bestretched in the same stretching conditions as those for a conventionalpolyamide resin containing no layered compound. Further, the firstinvention aims to provide a film in which a layered compound ishigh-dimensionally oriented, which has been conventionally thought to beimpossible, and thus to provide a biaxially stretched polyamide resinfilm having sufficient in-plane orientation while containing a largequantity of a layered inorganic compound. The resulting film isparticularly excellent in mechanical characteristics, a barrierproperty, heat resistance, dimensional stability, and a piercingproperty with little fluctuation of mechanical characteristics due tochanges in humidity.

The second invention aims to provide a biaxially stretched multilayerpolyamide resin film with suppressed boiling strains, excellentdimensional stability, and improved pinhole resistance. These improvedproperties can be provided by lowering the shrinkage stress caused atthe time of boiling by lowering the stress at the time of stretching andconsequently decreasing bowing of the film.

Means to Solve the Problems

Inventors of the invention thought that the easy formation of cracksalong a layered compound was due to stress in the perpendiculardirection to the plane of the layered compound as a result ofstretching. As a result, the inventors investigated the orientationstate of the layered compound and methods to decrease the stretchingstress and consequently, considered that in a conventional method, alarge stress was applied to the molecular chains in the width andthickness directions at the time of lengthwise stretching of a castsheet since the molecular chains were fixed by the layered compound andthus the successive high stretching in the width direction wasdifficult. Accordingly, the inventors developed a method for promotingorientation of the layered compound in the in-plane direction by evenlyapplying the shear stress to the sheet at the time of casting andthereby suppressing the formation of creases and cracks formed by stressconverged on the tip end of the layered compound. At the same time, themethod was capable of lowering the entanglement density in the thicknessdirection. The inventors further made investigations in detail on causesof decreasing the stretching property. Accordingly, paying attention tothe in-plane orientation of the dispersed inorganic layered compoundbesides the resin of the matrix and referring to the report by Nishinoet al, the inventors of the invention quantitatively measured theorientation degree of the layered compound and investigated therelationship of characteristics. It was consequently found that in afilm obtained by employing such methods, a layered compound could beoriented in a very high level and that a film contained a layeredcompound oriented in a high level excellent characteristics, which aconventional film never had in the case the in-plane orientation degreemeasured from a half width of an x-ray diffraction peak derived from thedispersed layered compound became a specified value or higher, and thesefindings now lead to completion of the invention.

That is, the invention has the following configurations.

1. A biaxially stretched polyamide resin film containing 0.3 to 10 wt. %of an inorganic material including a layered compound, in which thelayered compound is in-plane oriented and the film has a haze of 1.0 to20%, an elastic modulus in the longitudinal direction of 1.7 to 3.5 GPaat a relative humidity of 35% RH, a surface roughness (Sa) of 0.01 to0.1 μm, and a static friction coefficient (F/B) of 0.3 to 1.0 at anormal stress of 0.5 N/cm².2. The biaxially stretched polyamide resin film as described in 1,wherein the number of pinholes after 1000 times Gelbo Flex test at 23°C. is 0 to 30.3. The biaxially stretched polyamide resin film as described in 1 or 2,wherein the film is transversely stretched at a transverse stretchingtemperature of 50 to 155° C.4. The biaxially stretched polyamide multilayer film as described in 1,wherein the film has a laminate structure of 8 or more layers in totaland a thickness of 3 to 200 μm, and the in-plane orientation degree ofthe inorganic layered compound measured by x-ray diffractometry is in arange of 0.4 to 1.0.5. The biaxially stretched polyamide multilayer film as described in 4,wherein a static mixer method is employed at the time of melt extrusionof a thermoplastic resin and the resin temperature immediately beforeintroduction into the static mixer is in a range from the melting pointto melting point +70° C. and the heater temperature in the latter halfof the static mixer is set to be higher by 5° C. or more and by 40° C.or less than the resin temperature immediately before introduction intothe static mixer.6. The biaxially stretched polyamide resin film as described in 1,wherein the layered compound is in-plane oriented and the in-planeorientation (ΔP) of the film is 0.057 to 0.075, and the value ofpiercing strength/thickness of the film is 0.88 to 2.50 (N/μm).7. The biaxially stretched polyamide resin film as described in 6,wherein the stretching ratio on the basis of an area by biaxialstretching measured as the product of the stretching ratio in thelengthwise direction and the stretching ratio in the transversedirection is 8.5 times or more.8. The biaxially stretched polyamide resin film as described in 6 or 7,wherein biaxial stretching is successive biaxial stretching inlengthwise stretching-transverse stretching order and when Ny is definedas a refractive index in the center part in the width direction of thefilm, the difference Ny(A)−Ny(B) between Ny(A) which is Ny of the sheetbefore lengthwise stretching and Ny(B) which is Ny of the sheet afteruniaxial stretching is 0.003 or higher.9. The biaxially stretched polyamide resin film as described in 1,wherein the film has a laminate structure of 8 or more layers, the filmis obtained by stretching as much as 2.5 to 5.0 times in thelongitudinal direction and 3.0 to 5.0 times in the width direction, andthe film has a ratio of the product (X1) of the maximum point stress(MPa) and a breaking elongation (%) of a sample stored at a humidity of40% for 12 hours and the product (X2) of the maximum point stress (MPa)and a breaking elongation (%) of a sample stored at a relative humidityof 80% for 12 hours is in a range of 1.0 to 1.5 when the maximum pointstress and breaking elongation is measured by a method as described inJIS K 7113 under conditions of a starting length of 40 mm, a width of 10mm, and a deformation rate of 200 mm/min after storage at an equilibriumwater absorption ratio of 3.0 to 7.0% and a relative humidity of 40%.10. A biaxially stretched multilayer polyamide resin film having 8 ormore layers in total and using a same resin composition for 80% based onthe ratio of the number of the layers, wherein the film is stretched 2.5to 5.0 times in the longitudinal direction of the film and has anin-plane orientation coefficient (ΔP) of 0.057 to 0.07 and a strain of0.1 to 2.0% after boiling treatment.11. The biaxially stretched multilayer polyamide resin film as describedin 10, wherein the film contains 0.3 to 10 wt. % of an inorganicmaterial containing a layered compound, the layered compound is in-planeoriented, and the oxygen permeation amount in conversion into 15 μm is0.05 to 18 cc.12. The biaxially stretched multilayer polyamide resin film as describedin 10 or 11, wherein at least one layer or more of resin layerscontaining a polyamide resin having a meta-xylylene skeleton as a maincomponent are laminated.

Effects of the Invention

According to the first invention, a polyamide resin containing a layeredcompound evenly dispersed therein, which conventionally has beenunderstood to be difficult to obtain with good strength and appearanceby a conventional stretching method, can be stretched evenly withoutdeteriorating the appearance. As a result, according to this method, itis possible to provide a polyamide resin film having an excellentslipping property under high humidity and with excellent surface gloss,which is generally difficult to be satisfactorily provided in a singlefilm.

Also, according to the first invention, it is made possible to provide afilm with excellent characteristics, particularly, a barrier property,mechanical characteristics, a piercing strength, and little strengthfluctuation in accordance with humidity levels, and that includes anano-composite resin containing a layered compound evenly dispersedtherein, which has been supposed to be difficult to obtain with goodstrength and appearance by a conventional stretching method.

Further, the occurrence of cleavage in the thickness direction of afilm, which is a problem with multi-layering, can be improved for amultilayer film obtained by a static mixer method by (i) keeping theresin temperature immediately before introduction into the static mixerin a range from the melting point to melting point +70° C. and (ii)keeping the heater temperature in the latter half of the static mixerhigher by 5° C. or more and by 40° C. or less than the resin temperatureimmediately before introduction into the static mixer.

According to the second invention, under the conditions for a monolayerpolyamide resin film, a resin sheet having a multilayer structure withthe same composition is stretched to give a film with reduced bowing andlittle boiling strain even at the end parts in the width direction.Also, use of a polyamide resin in which a layered compound is evenlydispersed provides a film excellent in not only the boiling strain butalso the barrier property and remarkably usable as a wrapping material.In addition, JP-A No. 2007-196635 is a patent application for amultilayer film; however it does not mention decrease of stress bymultilayer formation at the time of stretching in the publishedspecification and thus the invention is a fact which has not been known.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, at first, the first invention will be described in detail.

(Polyamide Resin)

A polyamide resin to be used in the invention is not particularlylimited and may include a ring-opening polymers of cyclic lactams,condensates of diamines and dicarboxylic acids, and self condensates ofamino acids. Typical examples are not particularly limited, but includenylon 6, nylon 7, nylon 66, nylon 11, nylon 12, nylon 4, nylon 46, nylon69, nylon 612, and m-xylylene diamine type nylon. Copolymer typepolyamide resins may be also used, such as aromatic polyamide resins,including nylon 6 and nylon 66 copolymerized with m-xylylenediamine,nylon 6T, nylon 6I, nylon 6/6T copolymers, nylon 6/6I copolymers, nylon6/polyalkylene glycol resins, nylon 11/polyalkylene glycol resins, nylon12/polyalkylene glycol resins, nylon 6/MXD 6 copolymers. Additionalusable resins are those obtained by copolymerization of other componentswith these resins and preferable examples are nylon 6, nylon 66, andm-xylylenediamine type nylon. Particularly, the gas permeability isremarkably decreased by laminating a few layers of a m-xylylenediaminetype nylon resin, and thus a m-xylylenediamine type nylon resin is apreferable embodiment.

Further, besides the polyamide resin described below, other resins andadditives may be added to these resins for use. Moreover, in terms ofthe economy, one preferred embodiment is use of a recovered filmproduced by the invention for a part or all of a polyamide resin. Usableexamples of other resins are conventionally known resins such aspolyester resins, polyurethane resins, acrylic resins, polycarbonateresins, polyolefin resins, polyester elastomer resins, and polyamideelastomer resins and not limited thereto.

(Layered Compound)

Examples of the layered compound are not limited to, but are layeredcompounds such as swelling mica, clay, montmorillonite, smectite,hydrotalcite, etc., which are usable regardless of being inorganic andorganic. The form of the layered compound is not particularly limited;however, a layered compound having an average length of the longerdiameter of 0.01 to 50 μm, preferably 0.03 to 20 μm, even morepreferably 0.05 to 12 μm and an aspect ratio of 5 to 5000, preferably 10to 5000 preferably is used. With respect to the aspect ratio of thelayered compound, in the case the aim for addition is improvement of thebarrier property, a layered compound with a high aspect ratio ispreferable. When the aim of addition is mechanical reinforcement, alayered compound with a low aspect ratio is preferable.

The addition amount of an inorganic material including a layeredcompound with respect to the above-mentioned polyamide resin ispreferably 0.3 to 10 wt. %. An inorganic layered compound is sometimesadded in the form of an organically treated layered compound, and theaddition amount and the content (addition amount) of the inorganicmaterial according to the weight residue described below do notnecessarily correspond with each other. Further, if a method formeasuring the inorganic material from the residue weight as describedbelow is employed, a small amount of an inorganic material other thanthe inorganic layered compound is added in some cases and in theinvention, it is calculated as the content of the inorganic materialincluding the layered compound. The content of the inorganic materialincluding the layered compound is a value calculated by subtracting theash from the residue weight measured by a thermogravimetric analyzer(TGA). In particular, the content is calculated by measuring the residueweight after increasing the temperature of a resin containing a layeredcompound from room temperature to 550° C. and thereafter subtracting thevalue of resin ash therefrom. In Example 1, the inorganic content can bemeasured to be 2.6% by subtracting 1.8% of residue weight derived fromthe resin from 4.4% of residue weight by TGA. Also, the ratio of anorganic treatment agent in the layered compound is separately measuredby TGA, and calculation using the numeral value can be employed. Thelower limit of the addition amount of the inorganic material including alayered compound is preferably 0.3%, furthermore preferably 0.7%, andeven more preferably 1.0%. If the addition amount is less than 0.3%, theeffect of the layered compound addition is slight in terms of thedimensional stability and mechanical characteristics, and thus it is notpreferable. Also, the static friction coefficient may be increased, andthe slipping property may be worsened. The upper limit is morepreferably 10% or less and furthermore preferably 8% or less. If theaddition amount is more than 10%, the effect in terms of the dimensionalstability and mechanical characteristics is saturated and it is noteconomical. Moreover, the fluidity at the time of melting is lowered,the surface roughness becomes unnecessarily significant, and the hazemay be lowered.

Common layered compounds may be used. Organically treated commercializedproducts preferably usable in a monomer insertion polymerization methoddescribed below are CLOISITE™ produced by Southern Clay Products Inc.,SOMASIF™ and LUCENTITE™ produced by Co-op Chemical Co., Ltd., and S-Benproduced by Hojun Yoko Co., Ltd.

(Thermoplastic Resin Containing Layered Compound Evenly DispersedTherein)

A thermoplastic resin containing a layered compound evenly dispersedtherein is commonly called a nano-composite resin. The layered compoundis preferably evenly dispersed and does not contain coarse matter with athickness exceeding 2 μm in the form of aggregates of the layeredcompound. In the case coarse matter with a thickness exceeding 2 μm isincluded in the layered compound, the transparency is lowered andstretching property of the resulting film is lowered, and therefore, itis not preferable.

The layered compound is preferable to be evenly dispersed in theabove-mentioned polyamide resin in the invention and the film productionmethod can be exemplified as follows.

1. Interlayer insertion method

1) monomer insertion polymerization method

2) polymer insertion method

3) organic lower molecule insertion (organic swelling) kneading method

2. In-situ method: In-situ filler formation method (sol-gel method)

3. Ultrafine particle direct dispersion method, etc.

Commercialized materials may include CRESS-ALON™ NF 3040 and NF 3020produced by Nanopolymer Composite Corp.; NCH 1015C2 produced by UbeIndustries Ltd.; and IMPERM™ 103 and IMPERM™ 105 produced by Nanocor,Inc. In order to heighten the dispersibility of the layered compound forsuppressing the formation of coarse matter in the layered compoundcontained in the polyamide resin, it is preferable to treat the layeredcompound with various kinds of organic treatment agents. However, toavoid an adverse effect of thermal decomposition of a treatment agent atthe time of melt molding, those obtained by using a low molecular weightcompound with high heat stability or by a method such as the monomerinsertion polymerization method in which a low molecular weight compoundis not used are preferable. With respect to the heat stability, atreated layered compound having a 5% weight loss temperature of 150° C.or higher is preferable. TGA or the like can be employed for themeasurement. In the case of a compound with inferior heat stability,foams may be formed in the film or coloring may be caused and therefore,it is not preferable (reference to “Challenging nano-technologicalmaterials: Polymer nano-composites in widened application development,”Sumitomo Bakelite-Tsutsunaka Techno Co., Ltd.).

The layered compound is preferably in-plane oriented in a film forexhibiting desirable characteristics. The in-plane orientation can beconfirmed by observing a cross section of the layered compound by atransmission electron microscope or a scanning electronic microscope.

(Film Formation Method)

In stretching of a resin containing a layered inorganic compound in theinvention, problems in the case of stretching by employing successivebiaxial stretching in lengthwise-transverse order, which is generallyadvantageous in terms of economy, are following three points: (1) in thestretching in the lengthwise direction (hereinafter, abbreviated as MD),crystallization proceeds due to the heat at the time of stretching andthe stretching property in the transverse direction (hereinafter,abbreviated as TD) is lost after uniaxial stretching; (2) breakingoccurs at the time of stretching in TD; and (3) breaking occurs at thetime of thermal fixation after stretching in TD. With respect to (1),when the MD stretching conditions in which the TD stretching is possibleand the MD stretching conditions in which the TD stretching isimpossible are put in order, it is found that the refractive index inthe width direction (refractive index in the y-axis, hereinafter,abbreviated as Ny) of a uniaxially stretched sheet after the MDstretching differs in each type of film. Concretely, it is found that Nyof a uniaxially stretched sheet, which is TD-stretchable, becomes lowafter the MD stretching. In contrast, Ny of a uniaxially stretchedsheet, which is not TD-stretchable (that is, whitened or broken at thetime of TD stretching), is scarcely changed or not at all changed afterthe MD stretching. It is found that in stretching of a common polyamideresin, Ny after the MD stretching becomes low simultaneously withoccurrence of neck-in in the width direction at the time of the MDstretching. On the other hand, in the case a layered compound is addedthereto, neck-in occurs, but Ny tends to be difficult to be low due tothe interaction of the layered compound and polyamide resin molecules.The phenomenon is supposedly attributed to as follows: since themolecular chains of a film before stretching are oriented at random inthe MD and TD directions, force is generated also in the TD direction atthe time of stretching the molecular chains in the MD direction by theMD stretching. The force applied also in the TD direction can bereleased by the neck-in in the TD direction in the case of stretching ofa common polyamide resin. On the other hand, in the case of thepolyamide resin containing a layered compound, since the molecularchains are cramped by the presence of the layered compound, the force inthe TD direction cannot be released and the molecular chains are put inthe state as if they are pulled also in the TD direction. Moreover, thelayered compound is rotated at the time of the MD stretching andtherefore, molecules are pulled also in directions other than the MDdirection. That is, the in-plane orientation is already in a high stateafter the MD stretching. Therefore, it is supposed that the stretchingstress at the time of successively carrying out the TD stretchingbecomes high and breaking is caused.

As a method for solving this problem, stretching conditions in which Nybecomes small after the MD stretching are employed to make the TDstretching at a high ratio possible without causing breaking in the TDstretching successively carried out thereafter. Thus, it is madepossible to produce a biaxially stretched polyamide resin film of theinvention on an industrial scale.

In the case Ny(A) is defined as the refractive index in the widthdirection before lengthwise stretching and Ny(B) is defined as therefractive index in the width direction after lengthwise stretching,Ny(A)−Ny(B) is preferably 0.001 or higher. It is more preferably 0.002or higher and most preferably 0.003 or higher.

As a method for lowering Ny after uniaxial stretching, a method ofconsiderably lowering the MD stretching rate can be employed. A similareffect can be produced by multi-layering an un-stretched sheet aftermelt extrusion. That is, the entanglement density of molecular chains islowered in the thickness direction by multi-layering and thus thedeformability of the molecular chains is improved and Ny can be lowered.As a result, an increase of in-plane orientation at the time of the MDstretching can be suppressed, and the TD stretching property can beimproved. The inventors have found that the biaxial stretching propertycan be improved by these methods and have completed a production methodwith high industrial applicability and a stretched film with excellentcharacteristics.

(Construction of Film)

The biaxially stretched polyamide resin film of the invention can beobtained essentially by stretching an un-stretched polyamide resin sheetcontaining a polyamide resin layer in which a layered compound is evenlydispersed. Basically a sheet with a monolayer construction is alsostretchable, however from an industrial viewpoint, it is preferable tostretch a multilayer sheet.

Hereinafter, a case of multilayer formation will be described. Withrespect to the number of all layers and the thickness of a layer, thelower limit of the number of layers is preferably not less than 8 layersand more preferably not less than 16 layers. The upper limit of thenumber of the layers is preferably not more than 10,000 layers and morepreferably not more than 5,000 layers. If the multilayer film is lessthan 8 layers, no stretching property improvement effect is exhibited,and the effect of the arrangement of the layered compound at the time ofmelt extrusion is lowered. On the other hand, if the multilayer filmexceeds 10,000 layers, the effect of stretching property improvement issaturated, and the heat shrinkage ratio is lowered.

The lower limit of the thickness of a layer is preferably 10 nm and morepreferably 100 nm in the state before stretching. If a layer is thinnerthan 10 nm, the crystal size in the layer becomes too small and the heatshrinkage ratio becomes high and therefore, it is not preferable.

The upper limit of the thickness of the layer is preferably not morethan 30 μm and more preferably not more than 20 μm. If a layer exceeds30 μm, the in-plane orientation of the layered compound in the statebefore stretching is low, and the effect on decreasing the stretchingstress is small, and therefore it is not preferable.

(Laminating Method)

Besides laminating different kinds of resin as employed commonly, it ispossible to layer the same kind of resin. Herein, although it seemsdifficult to find the physical meaning of multi-layering with the samekind resin by a method described below, in an actual system, aninterface of layers does not disappear even in the case of the sameresin is laminated by melt extrusion at the same temperature. Suchinterface exists even after stretching. The interface is the same asthat of a welded line of an injection-molded product, which is difficultto eliminate. As described, even when the same type resin is used, amultilayer state is maintained, and the entanglement of molecules in thethickness direction can be suppressed and kept low. A method forconfirming the existence of an interface of layers at the time oflaminating the same kind of resin by melt extrusion may be a method ofcooling a sample with ice or liquefied nitrogen, producing a crosssection by cutting the sample with a razor or the like thereafter,immersing the obtained sample in a solvent, such as acetone, andobserving the cross section with a microscope.

A polyamide resin and a resin composition composing other layers basedon necessity are supplied separately to respective extruders andextruded at a temperature higher than melting temperature. The meltingtemperature is preferably lower by 5° C. than the decomposition startingtemperature. Further, to suppress cracking of the layered compound inthe resin, the melting conditions and melting temperature have to be setcarefully. In the case of a polyamide resin with a high molecularweight, the layered compound is cracked if melting at such a lowtemperature as not higher than melting point +10° C. is carried out, andthe aspect ratio becomes smaller than that in the initial state. Thus,the effect of using a layered compound with a high aspect ratio isdiminished, and therefore, it is preferable to carry out melting at ahigh temperature in a range with no problem in terms of heat stability.

A polyamide resin and a resin composition composing other layers basedon necessity are laminated by various kinds of methods and a feed-blockmethod and a multi-manifold method can be employed. In the case of thefeed-block method, at the time of widening the width to the die widthafter laminating, if the melt viscosity difference between laminatedlayers and the temperature difference at the time of laminating aresignificant, the method results in laminating unevenness, deteriorationof the appearance, and unevenness of the thickness. Therefore, the meltviscosity difference between laminated layers and the temperaturedifference at the time of laminating should be carefully controlled atthe time of production. For suppression of occurrence of unevenness, itis preferable to control the melt viscosity at the time of extrusion by(1) lowering the temperature and (2) adding various kinds of additivessuch as polyfunctional epoxy compounds, isocyanate compounds,carbodiimide compounds, etc.

In the invention, promotion of orientation in the plane of the layeredcompound by the shear force at the time of laminating is also effectiveto suppress the breaking by convergence of the stress to the tip end ofthe layered compound at the time of stretching. As a method suitable forsuch a purpose, laminating by a feed block method and a static mixermethod is preferable and in terms of the simplicity of facilities, thestatic mixer method is particularly preferable.

In the case of multi-layering by the static mixer method, it ispreferable that the resin temperature immediately before introductioninto the static mixer is in a range from the melting point to meltingpoint +70° C., and that the heater temperature in the latter half of thestatic mixer is set to be in a range of higher by 5° C. or more and by40° C. or less than the resin temperature immediately beforeintroduction into the static mixer. If the resin temperature is lowerthan the melting point in the state before introduction into the staticmixer, the melt viscosity is too high, the appearance is deteriorated,and the laminated state is disordered. Further, if the resin temperatureis a temperature as high as the melting temperature +70° C. or higher,the melt viscosity is too low and the force needed for causing theabove-mentioned stretching effect of the layered compound becomes low.Moreover, it is preferable that the heater temperature in the latterhalf of the static mixer is set to be higher than the resin temperatureimmediately before introduction into the static mixer. If the heatertemperature difference is lower than 5° C., it results in appearancedeterioration, such as streaking unevenness and formation of a portionwith a thin thickness, which is a cause of breaking, and therefore, itis not preferable. If the heater temperature exceeds 40° C., the meltviscosity is too low and the force needed for causing theabove-mentioned stretching effect of the layered compound becomes lowand therefore, it is not preferable. The melting temperature differencebetween respective layers at the time of laminating a thermoplasticresin is 70° C. or lower, preferably 50° C. or lower, and morepreferably 30° C. or lower. The melt viscosity difference betweenrespective layers is within 30 times, preferably within 20 times, andmore preferably within 10 times at the estimated shear rate in a die, sothat appearance control at the time of laminating and unevennesssuppression are made possible. For adjustment of the melt viscosity,addition of the above-mentioned polyfunctional compounds can beemployed. The static mixer temperature or feed block temperature at thetime of laminating is indispensably lower than the 5% decompositiontemperature of the resin and further, it is in a range of preferablymelting point +20 to melting point +150° C., more preferably meltingpoint +30° C. to melting point +120° C., and most preferably meltingpoint +40° C. to melting point +110° C. When the feed block temperatureis too low, the melt viscosity becomes too high and the load on theextruder becomes too high and therefore, it is not preferable. When thetemperature is too high, the viscosity is too low and laminatingunevenness occurs and therefore, it is not preferable. Further, the filmafter biaxial stretching tends to have cleavage due to themulti-layering and in this case, the temperature of the latter half partof the static mixer and feed block and the temperature of dies are sosufficiently high as to increase the entanglement of the molecularchains in the interlayer and therefore it can be improved. Concretely,in the case of a static mixer, the cleavage suppression effect can beexhibited by increasing the outlet temperature to be higher by 5° C. to40° C. than the inlet temperature.

Further, laminating is possible by a multi-manifold method and theabove-mentioned problem of laminating unevenness is minimized. However,when laminating a layer with a melt viscosity difference, there occurs aproblem of a turning-around failure of the resins in the respectivelayers in the end parts and unevenness of the laminating ratio in theend parts in terms of productivity and also in this case, it ispreferable to control the melt viscosity difference.

For the die temperature, it is the same as described above and it is ina range of 150° C. to 300° C., preferably 170° C. to 290° C., and morepreferably 180° C. to 285° C. If the temperature becomes too low, themelt viscosity becomes too high and the surface roughening occurs toresult in appearance deterioration. If the temperature becomes too high,thermal decomposition of the resin is caused and, as described, the meltviscosity difference becomes wide and unevenness is caused andparticularly, unevenness with small pitches is caused.

With respect to each layer before stretching, the thickness of eachlayer is preferably in a range of 0.01 to 30 μm. If the thickness ofeach resin layer exceeds 30 μm, the effect of improving the stretchingproperty is lowered and therefore, it is not preferable for theinvention. If the thickness of each resin layer is less than 0.01 μm,the heat shrinkage ratio after thermal fixation becomes high and itbecomes difficult to keep good balance among various film properties,and therefore, it is not preferable.

(Stretching Method)

For a biaxially stretched polyamide resin film of the invention, anun-stretched sheet extruded by melt extrusion from a T die can bestretched by successive biaxial stretching or simultaneous biaxialstretching. In addition, a method such as a tubular manner can beemployed. However, to carry out sufficient orientation, a method using abiaxial stretching apparatus is preferable. In terms of thecharacteristics and economy, a preferable method is a method ofstretching in the lengthwise direction by a roll type stretchingapparatus and thereafter stretching in the transverse direction by atenter type stretching apparatus (successive biaxial stretching method).Further, with respect to the MD stretching, it is described above thatit is preferable to lower Ny at the time of the MD stretching forimproving the TD stretching property. In order to lower Ny whileincreasing the MD stretching ratio, it is preferable to employmulti-step MD stretching.

It is preferable to obtain the film by stretching a substantiallyun-oriented polyamide resin sheet obtained by melt extrusion from a Tdie 2.5 to 10 times as large as the film in the lengthwise direction ata temperature equal to or higher than the glass transition temperatureTg° C. of the polyamide resin and not higher than 150° C. Next, thelengthwise stretched film is stretched 3.0 to 10 times as large in thetransverse direction at a temperature of not lower than 50° C. and nothigher than 155° C. of polyamide resins. Next, the biaxially stretchedpolyamide resin film is thermally fixed in a temperature range of 150°C. to 250° C.

The heating crystallization temperature can be measured by increasingthe temperature of a sample resin which has been quenched after meltingby DSC.

In the MD stretching, if the temperature of the film is lower than theglass transition temperature (Tg) of the polyamide, problems of breakingand unevenness of the thickness due to the oriented crystallization bystretching occurs. On the other hand, if the film temperature exceeds150° C., breaking is caused due to the crystallization by heat. Further,if the stretching ratio in the MD stretching is less than 1.1 times,problems such as unevenness of the thickness and insufficient strengthin the lengthwise direction are caused. If the stretching ratio in theMD stretching exceeds 10 times, there occurs a problem that successiveTD stretching becomes difficult. The stretching ratio is preferably 3.0to 5.0 times.

When the film temperature in the TD stretching is a low temperature ofless than 50° C., the TD stretching property is bad and breaking occursand unevenness of the thickness in the TD direction attributed to theneck stretching becomes significant. When the film temperature is a hightemperature beyond (Tm)—20° C., unevenness of the thickness becomessignificant and therefore, it is not preferable. Further, if the TDstretching ratio is less than 1.1 times, unevenness of the thickness inthe TD direction becomes significant, the strength in the TD directionis lowered, and the in-plane orientation becomes inferior, which resultsin worsening of the characteristics not only in the TD direction butalso in the MD direction. The stretching ratio is preferably 3 times ormore. On the other hand, if the TD stretching ratio is a high ratiobeyond 10 times, practical stretching is difficult. The TD stretchingratio is preferably 3.0 to 5.0 times.

With respect to the stretching temperature, stretching at a lowtemperature is preferable in terms of sufficient exhibition of theaddition effect of the layered silicate, unevenness of thickness of thefilm, and Gelbo Flex resistance. A preferable condition may bestretching at a film temperature of 155° C. or lower at the time ofstretching.

Further, the film thickness after stretching is preferably in a range of3 to 200 μm. If the film thickness is lower than 3 μm, the handling ofthe film is worsened and therefore, it is not preferable. If the filmthickness exceeds 200 μm, the effect of inorganic composite formation isdiminished and therefore, it is not preferable.

A preferable production method of the invention may be a method bycutting both end parts of an un-stretched sheet, which is multi-layeredby a static mixer method or a feed block method, in the width directionby a method of cutting off based on necessity, adjusting the thicknessof each laminated layer to be 30 μm or thinner at the most end partbefore stretching, and thereafter carrying out stretching at least inone direction. In the above-mentioned multi-layer formation method,although depending on the structure of the dies, due to the imperfectionof division of the layers and the disorder of the layers at the time oflaminating, the number of the layers in the end part is sometimelessened and in this case, the layer thickness of the polyamide resincontaining a layered compound with an inferior stretching property in adispersed state may be inevitably increased. Therefore, the layerthickness becomes thicker than 30 μm and the stretching property of onlythe end part is considerably lowered and at the time of stretching, aphenomenon such as whitening and breaking is sometimes observed in theend part. In the invention, in such a case, to correct the layerthickness in the end part at the time of production to a desiredthickness, one preferable method is trimming the end part of anun-stretched sheet and thereafter carrying out stretching.

(Thermal Fixation)

In the case a thermal fixation temperature is a low temperature below150° C., the effect of dimensional stability improvement of the film byheat is slight and therefore, it is improper. On the other hand, in thecase of a high temperature exceeding 250° C., the appearance of the filmdegrades due to whitening attributed to thermal crystallization of thepolyamide and the mechanical strength is decreased, and therefore, it isimproper.

In addition, the density increase due to crystallization in the thermalfixation after the TD stretching and the accompanying volume shrinkageare caused, and in the case of the resin containing the layeredcompound, the stress to be generated is remarkably high and therefore,stress is applied in the MD direction by sharp heating and it sometimesresults in breaking. Therefore, as a heating method at the time ofthermal fixation, it is preferable to increase the heat quantity step bystep, and thus generation of acute shrinkage stress is suppressed. Aconcrete method is exemplified as a method of gradually increasing thetemperature or increasing the air blow amount toward the surrounding ofthe outlet from the surrounding of the inlet of a thermal fixation zone.Preferably, the air blow amount is gradually increased in terms of theheat shrinkage ratio after stretching and thermal fixation.

Further, with respect to the relaxation treatment, taking the balancewith the heat shrinkage ratio in the lengthwise direction intoconsideration, it is preferable to determine the relaxation ratio. Inthe invention, since the change of the dimensional stability withrespect to humidity in the lengthwise direction is small, the relaxationratio is preferably in a range of 0 to 5%. If the relaxation ratioexceeds 5%, the effect on decrease of the heat shrinkage ratio in thewidth direction is slight and therefore, it is not preferable.

Next, a method for considerably lowering the MD stretching rate asanother exemplified method will be described.

The method for considerably lowering the MD stretching rate ispreferable to lower the MD stretching rate of 2000%/min or less. It ismore preferably 1000%/min or less. In such a low rate MD stretching,since it is possible to carry out stretching while loosening themolecular chains cramped by the layered compound, it is contemplatedthat Ny is lowered after the MD stretching. In addition, the conditionsdescribed above can be employed for the temperature of the MDstretching, conditions of the TD stretching, and thermal fixationconditions.

A film obtained as described herein can be used industrially in variousapplications in form of a roll film wound around a paper tube or as itis or after being processed for, for instance, printing or lamination.The width of the roll film is preferably 30 cm or wider. The length ispreferably 500 m or longer. The upper limit of the width is about 600 cmand the upper limit of the length is about 20,000 m. Those films with awide width or a long length immediately after film formation can be slitin accordance with the use and commonly, used in form of a roll filmwith a width of 200 cm or narrower and a length of 8000 m or shorter.

(In-Plane Orientation of Polyamide Resin Film)

After the biaxial stretching, thermal fixation, and relaxationtreatment, the polyamide resin film of the invention has an in-planeorientation (ΔP) preferably 0.03 or higher, and more preferably 0.05 orhigher. The in-plane orientation can be measured by measuringbirefringence with a refractive index meter and carrying out acalculation according to the following expression:ΔP=(Nx+Ny)/2−Nz,wherein Nx is the refractive index in the longitudinal direction; Ny isthe refractive index in the width direction; and Nz is the refractiveindex in the thickness direction.

If ΔP exceeds 0.07, the productivity is lowered and therefore, it is notpreferable.

After the biaxial stretching, thermal fixation, and relaxationtreatment, the biaxially stretched polyamide resin film of the inventionhas an in-plane orientation (ΔP) of preferably 0.057 to 0.075 andparticularly preferably 0.059 to 0.07. The in-plane orientation can beincreased by increasing the biaxial stretching ratio, particularly theTD stretching ratio. If the in-plane orientation is less than 0.057, thepiercing strength of the film is lowered and therefore, it is notpreferable. Also, if the in-plane orientation exceeds 0.075, theproductivity is lowered and therefore, it is not so preferable.

(Film Characteristics—Piercing Strength)

The piercing strength of the biaxially stretched polyamide resin film ofthe invention is preferable to have a value satisfying a relationalexpression of piercing strength/thickness (N/μm)=0.80 to 2.0. If thepiercing strength is less than 0.80 N/μm, the piercing strength is lowand not preferable for the aim of the invention. Further, it is morepreferably 0.90 or higher. The upper limit is preferably 1.80 or lower.In the case of a production condition of exceeding 1.80, the operationalproperty is lowered and therefore, it is not preferable.

The piercing strength is improved by both of the effect of the layeredcompound and the effect of heightening the in-plane orientation. Forimprovement of the piercing strength, it is preferable to increase theaddition amount of the layered compound and simultaneously increase thein-plane orientation. It is preferable to satisfy at least the conditionthat the layered compound addition is 0.3% or more, and the in-planeorientation is 0.057 or higher. To obtain a film with a high piercingstrength, as described above, the stretching ratio based on the areaafter the biaxial stretching is adjusted to be preferably 8.5 times orhigher and further preferably 12 times or higher. If the stretchingratio based on the area is less than 8.5 times, the in-plane orientationis not heightened and the piercing strength is not improved. Also, thestretching ratio based on the area is preferably in a range of 8.5 to 40times, and if it exceeds 40 times, the operational property is worsened.

(Film Characteristic—In-Plane Orientation of Inorganic Layered Compound)

The film of the invention is improved in the heat resistance, barrierproperty, dimensional stability, and mechanical characteristics byhighly orienting the layered compound in the plane. The thermoplasticmultilayer film in the invention preferably has an in-plane orientationof the layered compound measured by x-ray diffractometry in a range of0.4 to 1.0. Herein, the in-plane orientation is a numeral valuecalculated from the half width of the (0n0) peak of the layered compoundaccording to the following expression:In-plane orientation=(180−half width)/180.If the in-plane orientation is less than 0.4, the in-plane orientationis low and the effect of the addition of the layered compound isdiminished and therefore, it is not preferable.

To increase the in-plane orientation of the layered compound, astretching ratio of 6 times or more based on the area is preferable, anda stretching ratio of 3 times or more in the transverse direction isfurther preferable. If the stretching ratio is less than 6 times basedon the area, the arrangement of the layered compound is insufficient andthe characteristic improvement effect is low. If the stretching ratioexceeds 50 times based on the area, the production difficulties exceedthe desired effect and therefore, it is not preferable in terms ofproductivity. To obtain a film having an in-plane orientation (ΔP) ofthe biaxially stretched polyamide resin film of the invention in a rangeof 0.057 to 0.075 and a value of the film piercing strength/thickness(N/μm) in a range of 0.88 to 2.0, with respect to the stretching ratioof the film, the stretching ratio based on the surface area afterbiaxial stretching, which is calculated as the product of the stretchingratios in the longitudinal direction and in the width direction, is in arange of preferably 8.5 to 40 times and more preferably 12 times ormore. If the stretching ratio based on the surface area is less than 8.5times, the in-plane orientation is not increased and the piercingstrength is not improved.

The multilayer stretched film containing the layered compound arrangedin the plane of the invention has excellent heat resistance andmechanical characteristics. With respect to the heat resistance, thetemperature at which the storage elastic modulus starts decreasing nearTg in dynamic viscoelasticity can be shifted to a high temperature sidein some cases. This is attributed to the reinforcing effect ofsuppressing the movement of the molecular chains of the thermoplasticresin by the layered compound. If the arrangement of the layeredcompound is insufficient, the effect is slight.

The multilayer stretched film containing the layered compound arrangedin the plane of the invention has an excellent oxygen barrier property.For example, when 0.3 to 15% as an addition amount of an inorganicmaterial including a layered compound is added to the polyamide resin,the oxygen permeability (20 to 25 cc/m²/day/atm) of the biaxiallystretched polyamide resin in conversion into 15 μm can be lowered toabout 5 to 15 cc/m²/day/atm. If the addition amount is less than 1%, thebarrier property improvement effect is slight and if the addition amountexceeds 10 wt. %, the barrier property improvement effect is saturatedand it is not economical. The same effect can be similarly be observedfor polyester resins and polypropylene resins.

(Film Characteristics—Haze)

The haze of the biaxially stretched polyamide resin film of theinvention is preferably in a range of 1.0 to 20%. If the haze at thetime of stretching is 1.0% or lower, stable production becomes difficultand therefore, it is not preferable. If the haze exceeds 20%, it becomesdifficult to see contents at the time of use. In addition, the designproperty is deteriorated and therefore, it is not preferable.

The haze in the invention is the total derived from the resin, theinorganic layered compound, and voids formed by separation of the resinfrom the inorganic layered compound surface at the time of stretching.It is preferable to decrease haze specifically derived from the voidsand in order to do that, the stretching conditions are carefully set.For example, when the MD temperature is too low, the haze is increaseddue to void formation and therefore, it is not preferable. When the TDtemperature is too high, haze increase is observed due tocrystallization and therefore, it is not preferable. A preferabletemperature range is as described above and can be adjusted withreference to these facts. Further, the temperature can be adjusted inaccordance with the size and type of the layered compound. For example,not only use of the layered compound with a size smaller than thewavelength of visible light makes the haze small but also use of thelayered compound with a refractive index close to that of the resinmakes the haze small.

(Film Characteristics—Surface Roughness, Static Friction Coefficient)

The biaxially stretched polyamide resin film of the invention ispreferable to have a static friction coefficient (F/B) within a range of0.3 to 1.0 at a normal stress of 0.5 N/cm² while having so extremelysmooth surface as to have a surface roughness (Sa) of 0.01 to 0.1 μm. Ingeneral, if the surface roughness is made low to heighten the surfacegloss, the static friction coefficient is increased and films will notslide on each other, particularly in a high humidity condition,resulting in various kinds of production troubles. However, the specificsurface smoothness and the slipping property are both satisfied bybiaxial stretching the polyamide resin containing an addition amount of0.3 to 10 wt. % of the inorganic material including a layered compoundin the invention at a sufficient area ratio. This is supposedlyattributed to that the effect of the layered compound addition can beexhibited at a high level and a high elastic modulus can be maintainedin a wide range from a low humidity to a high humidity. If the surfaceroughness is lower than 0.01, the slipping property is sometimesworsened and therefore, it is not preferable. Also, if the surfaceroughness exceeds 0.1 μm, the surface gloss is not different from thatof a system to which a common lubricant is added and it does not meetthe objective of the invention. In the case the static frictioncoefficient exceeds 1.0, the slipping property is worsened andtherefore, it is not preferable. The lower limit of the static frictioncoefficient is 0.3 or less.

The surface roughness can be increased by increasing the addition amountof the layered compound. The surface roughness also can be adjusted inaccordance with the size, form, or the like of the layered compound tobe added. The static friction coefficient can be adjusted by the surfaceroughness. In addition, the elastic modulus can be increased byincreasing the stretching ratio, particularly the stretching ratio inthe width direction, and the static friction coefficient can becontrolled accordingly.

Further, that the surface smoothness and the slipping property are bothsatisfied simultaneously without the need for a powder lubricant, suchas spherical silica, is a characteristic of the invention. However, thesurface roughness and the slipping property can be adjusted by adding apowder lubricant in accordance with the use. In the case of addition,the average particle diameter of the lubricant particles is preferably0.1 to 10 μm and more preferably 0.3 to 5 μm. The average value of theparticle diameter can be measured by measuring the diameter by anelectron microscope and calculating the average. The addition amount ispreferably 1000 ppm or lower and more preferably 700 ppm or lower.

If the average particle diameter is 0.1 μm or less, it is too small tochange the surface roughness and therefore, it is not preferable. In thecase particles with an average particle diameter exceeding 10 μm areused or in the case the addition amount exceeds 1000 ppm, it sometimesbecomes difficult to adjust the surface roughness to be 0.1 μm or lessand therefore, it is not preferable.

The surface roughness (Sa) can be properly adjusted to be 0.01 μm to 0.1μm with reference to the above-mentioned preferable ranges. Anadjustment method for preventing Sa from exceeding 0.1 μm may belessening the addition amount in the case the particle diameter islarge. In addition, particles with a large oil supply amount can beused, which is easy to be broken at the time of stretching in the casethe particles are agglomerates (secondary particles) of primaryparticles with a fine particle size; etc. As the particles, various kindparticles such as silica, alumina, zirconia, titania, crosslinkedacrylic beads, crosslinked styrene beads, benzoguanamine, etc. may beused.

(Equilibrium Moisture Content)

The equilibrium moisture content of the biaxially stretched multilayerpolyamide resin film of the invention is preferably in a range of 3.0 to7.0%. The equilibrium moisture content becomes higher than that of apolyamide resin film containing no layered compound, and it isattributed to that the layered compound has a high water absorptionproperty. The equilibrium moisture content is changed in accordance withthe addition amount of the layered compound and also changed inaccordance with the stretching conditions and it tends to be low alongwith increase of the in-plane orientation, so that the final equilibriummoisture content of the film can be determined by the addition amount ofthe layered compound and the stretching conditions. If the equilibriummoisture content is less than 3.0%, the elongation in a high humidity islowered and therefore, it is not preferable. Also, if the equilibriummoisture content exceeds 7%, water is evaporated at the time of dryingand a problem by water absorption may be caused at the time ofprocessing and therefore, it is not preferable.

(Maximum Point Stress, Elongation)

The biaxially stretched multilayer polyamide resin film of the inventionis preferable to have a ratio of the product (X1) of the maximum pointstress (MPa) and a breaking elongation (%) of a sample stored at ahumidity of 40% for 12 hours and a product (X2) at a humidity of 80% ina range of 1.0 to 1.5 when the maximum point stress and breakingelongation is measured by a method as described in JIS K 7113 underconditions of a starting length of 40 mm, a width of 10 mm, and adeformation rate of 200 mm/min after storage at a relative humidity of40%. It is said that the film toughness can be measured by calculatingthe area in the lower side of a stress-strain curve. A common nylon filmhas both high elongation and high maximum point stress under a highhumidity and is thus a film with extremely high ductility. On the otherhand, both maximum point stress and elongation are low at a low humidityand for practical purposes, it is impossible to design the mechanicalcharacteristics of a film in consideration of the effect of thehumidity. Contrarily, as compared with a common nylon film, theinventors of the invention have found that a film containing a layeredcompound oriented in the plane has characteristics scarcely changedunder a high humidity and is effective to increase the maximum pointstress under a low humidity. As a reason for this, it is assumed thatthe addition of a material with high hygroscopic property can reinforcethe mechanical characteristics under a low humidity. The hygroscopicproperty further provides proper mobility of molecular chains under ahigh humidity and thus prevents decrease of elongation or the like.

There is poly(ethylene terephthalate) as a film which is scarcelyaffected by humidity, and in this case, the ratio is around 1.0 and dueto the closeness to 1.0, with respect to the above-mentionedcharacteristic, it can be said that the film has low humiditydependence. If the ratio exceeds 1.5, the film become highlyhumidity-dependent just like a common nylon film and it does not meetthe aim of the invention. To make the ratio close to 1.0, theabove-mentioned stretching conditions, particularly the stretching ratioin the MD direction and the stretching ratio in the TD direction, areimportant.

More specifically, the MD stretching ratio is preferably 2.5 to 5.0times and more preferably 2.8 to 4.5 times. The MD stretching may be aone step or multi-step process. If the MD ratio is less than 2.8 times,the in-plane orientation after the biaxial stretching is not improved,and the mechanical characteristics at a low humidity are degraded. Ifthe MD ratio exceeds 5 times, not only are characteristics, such asboiling strain, are degraded, and the stability at the time ofstretching is lowered. The TD stretching ratio is preferably 3.0 to 6.0times. If the TD stretching ratio is less than 3.0 times, the maximumpoint stress in MD under a low humidity becomes low. In addition, sincethe in-plane orientation is degraded, the piercing strength and pinholeresistance are lowered. If the TD stretching ratio exceeds 6.0 times,the characteristics under a low humidity and a high humidity fluctuatesignificantly. The TD stretching ratio is more preferably 3.0 to 5.0times. In the invention, the stretching ratio on the basis of area ispreferably in a range of 6 to 25 times and more preferably in a range of9 to 22 times. If the stretching ratio on the basis of area is less than6 times, no sufficient in-plane orientation can be obtained and themechanical characteristics are degraded. If the stretching ratio on thebasis of area exceeds 25 times, the shrinkage stress is increased andboiling stress is worsened.

(Film Characteristics—Elastic Modulus in MD Direction)

The biaxially stretched polyamide resin film of the invention preferablyhas an elastic modulus in the longitudinal direction (MD) in a range of1.7 to 3.5 Gpa at a relative humidity of 35%. A polyamide resin filmcontaining no layered compound shows high elongation and high ductilityunder a high humidity and contrarily shows low elongation and tends tobe brittle under a low humidity. To increase the elastic modulus in theMD direction, it is necessary to heighten the stretching ratio not onlyin the MD direction but also in the TD direction, and thus there is alimit also in the stretching conditions. The biaxially stretchedpolyamide resin film described in the invention is enabled to keep theductility and suppress the lowering of the elastic modulus at a highhumidity and improve the elastic modulus and elongation at a lowhumidity. If the elastic modulus in MD is less than 1.7 GPa, theimprovement effect is slight. If the elastic modulus exceeds 3.5 GPa, itbecomes difficult to keep the balance with other characteristics.

(Film Characteristics—Heat Shrinkage Ratio)

The biaxially stretched polyamide resin film of the invention preferablyhas a heat shrinkage ratio at 160° C. for 10 minutes in a range of −3 to3% in both the lengthwise direction and transverse direction. In orderto make the heat shrinkage ratio close to zero, it is preferable tooptimize the stretching conditions, thermal fixation condition, and thethickness of the layer. For improvement of the stretching property, itis advantageous that the thickness of each layer is thin. However, ifthe layer is too thin, the heat shrinkage ratio cannot be lowered bythermal fixation. Therefore, the layer structure preferably is producedin accordance with the aimed heat shrinkage ratio. To satisfy both theheat shrinkage ratio and the stretching property simultaneously, thethickness of each layer before stretching is preferably in a range of 1to 30 μm and more preferably in a range of 2 to 20 μm. The lower limitof the heat shrinkage ratio is more preferably 0% or higher and evenmore preferably 0.1% or higher. The upper limit of the heat shrinkageratio is more preferably 3.0% or lower and even more preferably 2.5% orlower.

(Film Characteristics—Pinhole Resistance)

The biaxially stretched film in the invention has excellent pinholeresistance, and the number of pinholes after 1000 times Gelbo Flex testat 23° C. is preferably 0 to 30. The pinhole resistance is mainlyaffected by the stretching conditions and particularly, it is preferablethat the temperature at the time of TD stretching is increased not sohigh. In the case the TD stretching property is inferior, it issometimes required to increase the temperature. However, if thestretching temperature is increased too high beyond the low temperaturecrystallization temperature, partial crystallization is promoted withoutprogression of sufficient stretching and thickness unevenness andpinholes tend to be formed easily in fine regions. Also, pinholes caneasily form in the obtained film. With respect to the TD stretchingtemperature, it is preferably 155° C. or lower. If the TD stretchingtemperature exceeds 155° C., the film tends to become brittle, and thepinhole resistance is worsened.

(Film Characteristics—Dimensional Change Ratio and Oxygen Permeability)

The biaxially stretched polyamide resin film in the invention ispreferable to have a dimensional change ratio in both the lengthwise andtransverse directions in a range of 0.1 to 1.0% at 25° C. and relativehumidity of 35% and at 25° C. and relative humidity of 85%. The heatshrinkage ratio and the hygroscopic dimensional change ratio in thewidth direction can be slightly adjusted in accordance of the relaxationratio in the width direction at the time of thermal fixation. However,the heat shrinkage ratio and hygroscopic dimensional change ratio areessential issues in the lengthwise direction and particularly in thesuccessive biaxial stretching, it is very difficult to lower thehygroscopic dimensional change ratio while taking the balance of othercharacteristics into consideration. It is pointed out that aconventional polyamide resin tends to easily cause the dimensionalchange because of the disconnection of hydrogen bonds formed by theamide groups among the molecular chains by water. However, the polyamideresin in which the layered compound is evenly dispersed suppressed theeffect of water due to the interaction of the layered compound and theamide groups in the molecular chains. It can be assumed that thehygroscopic dimensional change can be suppressed by using them; however,since conventionally there has been no proper stretching method, it isnot actually achieved. It is made possible to provide highly advanceddimensional stability at the time of moisture absorption by stretchingthe sheet with a multilayer structure in the invention.

The biaxially stretched polyamide resin film in the invention containsthe layered compound oriented in the plane and has an excellent barrierproperty with an oxygen permeability in conversion into 15 μm preferablyin a range of 5 to 20 cc/m²/day/atm. The upper limit of the oxygenpermeability is preferably 19 cc/m²/day/atm or lower, and morepreferably 18 cc/m²/day/atm or lower. Since the oxygen barrier propertydepends on the addition amount of the layered compound in the polyamideresin (X) and (Y), the addition amount of the layered compound ispreferably in a range of 2 to 20 wt. % in the entire film. If theaddition amount is less than 2 wt. %, the effect of the barrier propertyis slight, and if the addition amount exceeds 20 wt. %, the effect ofbarrier property improvement is saturated and it is not economical.

The biaxially stretched polyamide resin film of the invention may besubjected to corona treatment, coating treatment, or flame treatment toimprove the adhesiveness and wettability in accordance with use. Withrespect to the coating treatment, an in-line coating method ofstretching a coated product during film formation is preferably used.The biaxially stretched polyamide resin film of the invention isgenerally further processed by printing, deposition, lamination, etc. inaccordance with the desired end use.

The biaxially stretched polyamide resin film of the invention mayoptionally contain a hydrolysis resistant improver, an antioxidant, acoloring agent (a pigment, a dye), an antistatic agent, a conductiveagent, a flame retardant, a reinforcing agent, an organic lubricant, anucleating agent, a release agent, a plasticizer, an adhesive aid, apressure-sensitive adhesive, etc.

Next, the second invention will be described in detail.

Besides increasing the heat resistance of a resin, it is effective tolower the shrinkage stress at the time of boiling. The inventors of theinvention have found that the stretching stress can be lowered bylowering the entanglement density of molecular chains in the thicknessdirection by a multilayer formation and thereby improving the ease ofdeformation of the molecular chains. As a result, the shrinkage stresscan be lowered in spite of in-plane orientation same as that of a filmwith a monolayer structure. Also, the inventors have found that thesemethods can lower the bowing of the film, and that it is possible toprovide a production method with high industrial applicability and astretched film with excellent characteristics.

(Polyamide Resin)

A polyamide resin to be used in the invention is not particularlylimited and may include a ring-opening polymers of cyclic lactams,condensates of diamines and dicarboxylic acids, and self condensates ofamino acids. Suitable examples are not particularly limited, but includenylon 6, nylon 7, nylon 66, nylon 11, nylon 12, nylon 4, nylon 46, nylon69, nylon 612, and m-xylylene diamine type nylon. Copolymer typepolyamide resins may be also used, such as aromatic polyamide resins,including nylon 6 and nylon 66 copolymerized with m-xylylenediamine,nylon 6T, nylon 6I, nylon 6/6T copolymers, nylon 6/6I copolymers, nylon6/polyalkylene glycol resins, nylon 11/polyalkylene glycol resins, nylon12/polyalkylene glycol resins, nylon 6/MXD 6 copolymers. Other usableresins are those obtained by copolymerization of other components withthese resins and preferable examples are nylon 6, nylon 66, andm-xylylenediamine type nylon. Particularly, the gas permeability isremarkably decreased by laminating a few layers of a m-xylylenediaminetype nylon resin, and thus it is preferably used.

Further, besides polyamide resin described below, other resins andadditives may be added to these resins for use. Moreover, in terms ofthe economy, it is preferable to use a recovered film produced by theinvention for a part or all of a polyamide resin. Usable examples ofother resins are conventionally known resins such as polyester resins,polyurethane resins, acrylic resins, polycarbonate resins, polyolefinresins, polyester elastomer resins, and polyamide elastomer resins andnot limited thereto.

With respect to the slipping property, various kinds of lubricants maybe added to provide surface roughness, and both organic type lubricantsand inorganic type lubricants can be used. Although not particularlylimited in the invention, a sufficient slipping property can be providedwithout addition of these lubricants in the invention. The lubricanttype to be added and the addition amount should be determined takinginto account the various kinds of characteristics. In the case of aninorganic type lubricant, the particle diameter is preferably 0.5 μm orlarger and more preferably 1 μm or larger. The addition amount ispreferably in a range of 100 to 5000 ppm in the layer forming thesurface layer. If the addition amount is less than 100 ppm, the additioneffect is slight. If the addition amount exceeds 5000 ppm, the effect issaturated and therefore, it is not economical.

(Polyamide Resin Containing Layered Compound Evenly Dispersed Therein)

In the invention, besides a common polyamide resin, a polyamide resincontaining a layered compound evenly dispersed therein, described below,can be used. In this case, the heat resistance, barrier property, andhygroscopic strain of a resin can be improved.

The polyamide resin containing layered compound evenly dispersed thereinis commonly called nano-composite nylon. Typically, the layered compoundis evenly dispersed and preferably contains no coarse material largerthan 2 μm thickness. When the coarse material larger than 2 μm iscontained, the transparency is lowered and the stretching property isdeteriorated and therefore, it is not preferable.

Examples of the layered compound are not limited to, but are layeredcompounds, such as swelling mica, clay, montmorillonite, smectite,hydrotalcite, etc., which are usable regardless of being inorganic andorganic. The form of the layered compound is not particularly limited.However, a layered compound having an average length of the longerdiameter of 0.01 to 50 μm, preferably 0.03 to 20 μm, even morepreferably 0.05 to 12 μm and an aspect ratio of 5 to 5000, preferably 10to 5000 are preferably used. The addition amount of an inorganic layeredcompound with respect to the above-mentioned polyamide resin ispreferably 0.3 to 10 wt. %. An inorganic layered compound is sometimesadded in the form of an organically treated layered compound and theaddition amount and the content (addition amount) of the inorganicmaterial according to the weight residue described below do notnecessarily correspond with each other. Further, if a method formeasuring it from the residue weight as described below is employed, asmall amount of an inorganic material other than the inorganic layeredcompound is added in some cases and in the invention, it is calculatedas the content of the inorganic material including the layered compound.The content of the inorganic material including the layered compound isa value calculated by subtracting the ash from the residue weightmeasured by a thermogravimetric analyzer (TGA). More specifically, theaddition amount is calculated by measuring the residue weight afterincreasing the temperature of a resin containing a layered compound fromroom temperature to 550° C. and thereafter subtracting the value ofresin ash therefrom. In Example 1, the inorganic content can be measuredto be 2.6% by subtracting 1.8% of residue weight derived from the resinfrom 4.4% of residue weight by TGA. Also, the ratio of an organictreatment agent in the layered compound is separately measured by TGA,and calculation using the numeral value can be employed.

The lower limit of the content of the layered compound is morepreferably 0.3%, furthermore preferably 0.5%, and most preferably 0.7%.If the addition amount is less than 1.0%, the effect of the layeredcompound addition is slight in terms of the slight effect on thedimensional stability and mechanical characteristics. Also, the staticfriction coefficient may be increased and the slipping property may beworsened.

The upper limit of the addition amount is more preferably 10% or lessand furthermore preferably 8% or less. If the addition amount is morethan 10%, the effect on the dimensional stability and mechanicalcharacteristics is saturated and it is not economical and the fluidityat the time of melting is lowered. Further, the surface roughnessbecomes unnecessarily significant, and the haze may be lowered.

Common layered compounds may be used and organically treatedcommercialized products preferably usable in a monomer insertionpolymerization method described below are CLOISITE™ produced by SouthernClay Products Inc., SOMASIF™ and LUCENTITE™ produced by Co-op ChemicalCo., Ltd., and S-Ben produced by Hojun Yoko Co., Ltd.

The layered compound is preferable to be evenly dispersed in theabove-mentioned polyamide resin in the invention. The film productionmethod can be exemplified as follows.

1. Interlayer insertion method

1) monomer insertion polymerization method

2) polymer insertion method

3) lower organic molecule insertion (organic swelling) kneading method

2. In-situ method: In-situ filler formation method (sol-gel method)

3. Ultrafine particle direct dispersion method, etc.

Commercialized materials may include CRESS-ALON™ NF 3040 and NF 3020produced by Nanopolymer Composite Corp.; NCH 1015C2 produced by UbeIndustries Ltd.; and IMPERM™ 103 and IMPERM™ 105 produced by Nanocor,Inc. In order to increase the dispersibility of the layered compound forsuppressing the formation of coarse matter in the layered compoundcontained in the polyamide resin, it is preferable to treat the layeredcompound with various kinds of organic treatment agents. However, toavoid an adverse effect of thermal decomposition of a treatment agent atthe time of melt molding, those obtained by using a low molecular weightcompound with high heat stability or by a method such as the monomerinsertion polymerization method in which a low molecular weight compoundis not used are preferable. With respect to the heat stability, atreated layered compound having a 5% weight loss temperature of 150° C.or higher is preferable. TGA or the like can be employed for themeasurement. In the case of a compound with inferior heat stability,foams may be formed in the film or coloring may be caused and therefore,it is not preferable (reference to “Challenging nano-technologicalmaterials: Polymer nano-composites in widened application developments,”Sumitomo Bakelite-Tsutsunaka Techno Co., Ltd.).

The layered compound is preferably in-plane oriented in a film forexhibiting desirable characteristics. The in-plane orientation can beconfirmed by observing a cross section of the layered compound by atransmission electron microscope or a scanning electronic microscope.

(Film Formation Method)

The biaxially stretched multilayer polyamide resin film of the inventioncan be produced by a common method and obtained by stretching amultilayer un-stretched sheet obtained by various methods in the sameconditions as those in a common case, and the thickness of each layerand the stretching conditions are controlled to give a prescribedin-plane orientation, so that a film with little boiling strain andexcellent in various characteristics can be obtained. The effect of themultilayer formation is based on that the stretching stress andconsequently shrinkage stress at the time of boiling are lowered bydecreasing the entanglement of molecular chains in the thicknessdirection and as a result, bowing is lessened and the boiling strain isdecreased.

Hereinafter, the system of addition of a layered inorganic compound willbe described. In stretching of a resin containing a layered inorganiccompound, problems in the case of stretching by employing successivebiaxial stretching in lengthwise-transverse order, which is generallyadvantageous in terms of economy, are following three points: (1) in thestretching in the lengthwise direction (hereinafter, abbreviated as MD),crystallization proceeds due to the heat at the time of stretching andthe stretching property in the transverse direction (hereinafter,abbreviated as TD) is lost after uniaxial stretching; (2) breakingoccurs at the time of stretching in TD; and (3) breaking occurs at thetime of thermal fixation after stretching in TD. With respect to (1),when the MD stretching conditions in which the TD stretching is possibleand the MD stretching conditions in which the TD stretching isimpossible are put in order, it is found that the refractive index inthe width direction (refractive index in the y-axis, hereinafter,abbreviated as Ny) of a uniaxially stretched sheet after the MDstretching differs in each type of film. Concretely, it is found that Nyof a uniaxially stretched sheet which is TD-stretchable becomes lowafter the MD stretching. In contrast, Ny of a uniaxially stretched sheetwhich is not TD-stretchable (that is, whitened or broken at the time ofTD stretching) is scarcely changed or not at all changed after the MDstretching. It is found that in stretching of a common polyamide resin,Ny after the MD stretching becomes low simultaneously with occurrence ofneck-in in the width direction at the time of the MD stretching. On theother hand, in the case a layered compound is added thereto, neck-inoccurs, but Ny tends to be difficult to be low due to the interaction ofthe layered compound and polyamide resin molecules. The phenomenon issupposedly attributed to as follows: since the molecular chains of afilm before stretching are oriented at random in the MD and TDdirections, force is generated also in the TD direction at the time ofstretching the molecular chains in the MD direction by the MDstretching. The force applied also in the TD direction can be releasedby the neck-in in the TD direction in the case of stretching of a commonpolyamide resin. On the other hand, in the case of the polyamide resincontaining a layered compound, since the molecular chains are cramped bythe presence of the layered compound, the force in the TD directioncannot be released and the molecular chains are put in the state as ifthey are pulled also in the TD direction. Moreover, the layered compoundis rotated at the time of the MD stretching and therefore, molecules arepulled also in directions other than the MD direction. That is, thein-plane orientation is already in a high state after the MD stretching.Therefore, it is supposed that the stretching stress at the time ofsuccessively carrying out the TD stretching becomes high and breaking iscaused.

As a method for solving this problem, stretching conditions in which Nybecomes small after the MD stretching are employed to make the TDstretching at a high ratio possible without causing breaking in the TDstretching successively carried out thereafter. Thus, it is madepossible to produce a film of the invention on an industrial scale.

In the case Ny(A) is defined as the refractive index in the widthdirection before lengthwise stretching and Ny(B) is defined as therefractive index in the width direction after lengthwise stretching,Ny(A)−Ny(B) is preferably 0.001 or higher. It is more preferably 0.002or higher and most preferably 0.003 or higher.

As a method for lowering Ny after uniaxial stretching, a method ofconsiderably lowering the MD stretching rate can be employed. A similareffect can be produced by multi-layering an un-stretched sheet aftermelt extrusion. That is, the entanglement density of molecular chains islowered in the thickness direction by multi-layering and thus thedeformability of the molecular chains is improved and Ny can be lowered.As a result, an increase of in-plane orientation at the time of the MDstretching can be suppressed, and the TD stretching property can beimproved. The inventors have found that the biaxial stretching propertycan be improved by these methods and have completed a production methodwith high industrial applicability and a stretched film with excellentcharacteristics.

(Construction of Film)

The biaxially stretched multilayer polyamide resin film of the inventioncan be obtained essentially by stretching an un-stretched multilayerpolyamide resin sheet having 8 layers or more in total.

In the invention, the number of layers is preferably at least not lessthan 8 layers and more preferably not less than 16 layers. If themultilayer film is less than 8 layers, the effect of lowering theentanglement density in the thickness direction is slight and the effectof lowering the boiling strain is slight and therefore, it is notpreferable. The conditions of the number of the layers is preferably notmore than 10,000 layers and more preferably 5,000 layers. If themultilayer film exceeds 10,000 layers, the heat shrinkage ratio afterthe thermal fixation is not lowered.

The thickness of each layer before stretching is preferably 10 nm to 30μm and more preferably 100 nm to 10 μm. If a layer is thinner than 10nm, the heat shrinkage ratio after the thermal fixation is not loweredand therefore, it is not preferable. If a layer exceeds 30 μm, theeffect of lowering the entanglement density in the thickness directionis slight, and the effect of lowering the boiling strain is slight andtherefore, it is not preferable.

With respect to the biaxially stretched multilayer polyamide resin filmof the invention, 80% or more layers preferably contain the same resincomposition. If less than 80% of the layers do not contain the sameresin composition, the effect of the shrinkage stress derived fromanother resin layer becomes significant, resulting a diminished effectof decreasing the shrinkage stress and a diminished effect of decreasingthe boil strain and therefore, it is not preferable.

(Laminating Method)

Besides laminating different kinds of resin as employed commonly, it ispossible to layer the same kind of resin. Herein, although it seemsdifficult to find the physical meaning of multi-layering with the samekind of resin by a method described below, in an actual system, aninterface of layers does not disappear even in the case of the sameresin is laminated by melt extrusion at the same temperature. Suchinterface exists even after stretching. The interface is the same asthat of a welded line of an injection-molded product, which is difficultto eliminate. As described, even when the same type of resin is used, amultilayer state is maintained and the entanglement of molecules in thethickness direction can be suppressed and kept low. A method forconfirming the existence of an interface of layers at the time oflaminating the same kind of resin by melt extrusion may be a method ofcooling a sample with ice or liquefied nitrogen, producing a crosssection by cutting the sample with a razor or the like thereafter,immersing the obtained sample in a solvent such as acetone, andobserving the cross section with a microscope.

A polyamide resin and a resin composition composing other layers basedon necessity are supplied separately to respective extruders andextruded at a temperature higher than melting temperature. The meltingtemperature is preferably lower by 5° C. than the decomposition startingtemperature. Further, in the case of using a resin containing thelayered compound, to suppress cracking of the layered compound in theresin, the melting conditions and melting temperature have to be setcarefully. In the case of a polyamide resin with a high molecularweight, the layered compound is cracked if melting at such a lowtemperature as not higher than melting point +10° C. is carried out, andthe aspect ratio becomes smaller than that in the initial state. Thus,the effect of using a layered compound with a high aspect ratio isdiminished, and therefore, it is preferable to carry out melting at ahigh temperature in a range with no problem in terms of heat stability.

A polyamide resin and a resin composition composing other layers basedon necessity are laminated by various kinds of methods and a feed-blockmethod and a multi-manifold method can be employed. In the case of thefeed-block method, at the time of widening the width to the die widthafter laminating, if the melt viscosity difference between laminatedlayers and the temperature difference at the time of laminating aresignificant, the method results in laminating unevenness, deteriorationof the appearance, and unevenness of the thickness. Therefore, the meltviscosity difference between laminated layers and the temperaturedifference at the time of laminating should be carefully controlled atthe time of production. For suppression of occurrence of unevenness, itis preferable to control the melt viscosity at the time of extrusion by(1) lowering the temperature and (2) adding various kinds of additivessuch as polyfunctional epoxy compounds, isocyanate compounds,carbodiimide compounds, etc.

In the invention, promotion of orientation in the plane of the layeredcompound by the shear force at the time of laminating is also effectiveto suppress the breaking by convergence of the stress to the tip end ofthe layered compound at the time of stretching. As a method suitable forsuch a purpose, laminating by a feed block method and a static mixermethod is preferable.

The melting temperature difference between respective layers at the timeof laminating of the polyamide resin is 70° C. or lower, preferably 50°C. or lower, and more preferably 30° C. or lower. The melt viscositydifference of resins between layers is adjusted to be within 30 times,preferably within 20 times, and more preferably within 10 times at theestimated shear rate in a die, so that the appearance control at thetime of laminating and unevenness suppression can be made possible. Forthe adjustment of the melt viscosity, addition of the above-mentionedpolyfunctional compounds can be employed. The static mixer temperatureor feed block temperature at the time of laminating is in a range of150° C. to 330° C., preferably 170° C. to 220° C., and more preferably180° C. to 300° C. Since the laminating state becomes better as theviscosity is higher at the time of laminating, the feed blocktemperature and static mixer temperature is more preferable as beinglower; however if the feed block temperature and static mixertemperature is too low, the melt viscosity becomes too high and the loadon the extruder becomes too high and therefore, it is not preferable. Ifthe temperature is too high, the viscosity is too low and laminatingunevenness occurs and therefore, it is not preferable.

Further, laminating is possible by a multi-manifold method and theabove-mentioned problem of laminating unevenness is hardly caused.However, in the case of laminating a layer with a melt viscositydifference, there occurs a problem of a turning-around failure of theresins in the respective layers in the end parts and unevenness of thelaminating ratio in the end parts in terms of productivity and also inthis case, it is preferable to control the melt viscosity difference.

For the die temperature, it is the same as described above and it is ina range of 150° C. to 300° C., preferably 170° C. to 290° C., and morepreferably 180° C. to 285° C. If the die temperature becomes too low,the melt viscosity becomes too high and the surface roughening occurs toresult in appearance deterioration. If the die temperature becomes toohigh, thermal decomposition of the resin is caused and, as described,the melt viscosity difference becomes wide and unevenness is caused andparticularly, unevenness with small pitches is caused.

(Stretching Method)

For a biaxially stretched multilayer polyamide resin film of theinvention, an un-stretched sheet extruded by melt extrusion from a T diecan be stretched by successive biaxial stretching and simultaneousbiaxial stretching. In addition, a method such as a tubular manner canbe employed. However, to carry out sufficient orientation, a methodusing a biaxial stretching apparatus is preferable. In terms of thecharacteristics and economy, a preferable method is a method ofstretching in the lengthwise method by a roll type stretching apparatusand thereafter stretching in the transverse direction by a tenter typestretching apparatus (successive biaxial stretching method). Further,with respect to the MD stretching, since it is preferable to lower MDorientation at the time of the MD stretching for lessening bowing, it ispreferable to employ multi-step MD stretching.

It is preferable to obtain the film by stretching a substantiallyun-oriented polyamide resin sheet obtained by melt extrusion from a Tdie 2.5 to 10 times as large as the film in the lengthwise direction ata temperature equal to or higher than the glass transition temperatureTg° C. of the polyamide resin and not higher than 150° C. Next, thelengthwise stretched film is stretched 3.0 to 10 times as large at atemperature of not lower than 50° C. and not higher than 155° C. Next,the biaxially stretched polyamide resin film is thermally fixed in atemperature range of 150° C. to 250° C.

The heating crystallization temperature can be measured by increasingthe temperature of a sample resin which has been quenched after meltingby DSC.

In the MD stretching, if the temperature of the film is lower than theglass transition temperature Tg° C. of the polyamide, problems ofbreaking and unevenness of the thickness due to the orientedcrystallization by stretching occurs. On the other hand, if the filmtemperature exceeds 150° C., breaking is caused due to thecrystallization by heat. Further, the stretching ratio of the MDstretching in the invention is preferably 2.5 to 5.0 times and morepreferably 2.8 to 4.5 times. If the stretching ratio of the MDstretching is less than 2.5 times, problems such as unevenness of thethickness and insufficient strength in the lengthwise direction arecaused. If the stretching ratio in the MD stretching exceeds 5 times,the effect for decreasing the boiling strain is diminished andtherefore, it is not preferable. The MD stretching may be one-step ormulti-step process.

When the film temperature in the TD stretching is a lower than 50° C.,the TD stretching property is bad and breaking occurs and unevenness ofthe thickness in the TD direction attributed to the neck stretchingbecomes significant. When the film temperature is a high temperaturebeyond 155° C., unevenness of the thickness becomes significant.Further, if the TD stretching ratio is less than 1.1 times, unevennessof the thickness in the TD direction becomes significant and it is notpreferable and the strength in the TD direction is lowered, and thein-plane orientation becomes inferior, which results in worsening of thecharacteristics not only in the TD direction but also in the MDdirection. The stretching ratio is therefore preferably 3 times or more.On the other hand, if the TD stretching ratio is a high ratio beyond 10times, practical stretching is difficult. The TD stretching ratio ispreferably 3.0 to 5.0 times.

The stretching ratio based on the area at the time of producing thebiaxially stretched multilayer polyamide resin film of the invention ispreferably in a range of 6 to 25 times and more preferably in a range of9 to 22 times. If the stretching ratio based on the area is lower than 6times, sufficient in-plane orientation cannot be done and the mechanicalcharacteristics are degraded and therefore, it is not preferable. On theother hand, if the stretching ratio based on the area exceeds 25 times,the shrinkage stress becomes significant and the boiling strain cannotbe diminished and therefore, it is not preferable.

With respect to the stretching temperature, stretching at a lowtemperature is preferable in terms of sufficient exhibition of theaddition effect of the layered silicate, unevenness of thickness of thefilm, and Gelbo Flex resistance. A preferable condition may bestretching at a film temperature of 155° C. or lower at the time ofstretching.

(Thermal Fixation)

In the case a thermal fixation temperature is a low temperature below150° C., the thermal fixation effect of the film by heat is slight andtherefore, it is improper. On the other hand, in the case of a hightemperature exceeding 250° C., the appearance of the film degrades dueto whitening attributed to thermal crystallization of the polyamide andthe mechanical strength is decreased, and therefore, it is improper.

In addition, in the system containing the layered compound, the densityincrease due to crystallization in the thermal fixation after the TDstretching and the accompanying volume shrinkage are caused, and in thecase of the resin containing the layered compound, the stress to begenerated is remarkably high and therefore, stress is applied in the MDdirection by sharp heating and it sometimes results in breaking.Therefore, as a heating method at the time of thermal fixation, it ispreferable to increase the heat quantity step by step and thusgeneration of acute shrinkage stress is suppressed. A concrete method isexemplified as a method of gradually increasing the temperature orincreasing the air blow amount toward the surrounding of the outlet fromthe surrounding of the inlet of a thermal fixation zone. Preferably, theair blow amount is gradually increased in terms of the thermal shrinkageratio after stretching and thermal fixation.

Further, with respect to the relaxation treatment, taking the balancewith the heat shrinkage ratio into consideration, it is preferable todetermine the relaxation ratio. In the invention, since the dimensionalstability with respect to humidity in the lengthwise direction is small,the relaxation ratio is preferably in a range of 0 to 5%. If therelaxation ratio exceeds 5%, the effect on decrease of the heatshrinkage ratio in the width direction is slight and therefore, it isnot preferable.

(In-Plane Orientation)

After the biaxial stretching, thermal fixation, and relaxationtreatment, the biaxially stretched multilayer polyamide resin film ofthe invention has an in-plane orientation (ΔP) of preferably 0.057 to0.07. The in-plane orientation can be measured by measuringbirefringence with a refractive index meter and carrying out calculationaccording to the following expression:ΔP=(Nx+Ny)/2−Nz,wherein Nx is the refractive index in the longitudinal direction; Ny isthe refractive index in the width direction; and Nz is the refractiveindex in the thickness direction.

The in-plane orientation can be increased by increasing the biaxialstretching ratio, particularly the TD stretching ratio and if thein-plane orientation is less than 0.057, the mechanical strength such asthe piercing strength of the film is lowered and therefore, it is notpreferable. Further, if the in-plane orientation exceeds 0.07, theproductivity is lowered and therefore, it is not preferable.

(Boiling Strain)

The boiling strain of the biaxially stretched multilayer polyamide resinfilm in the invention is preferably 0.1 to 2.0%. The boiling strain iscaused by fixation of the end parts in relation to the shrinkage in thecenter part at the time of TD stretching and it is considerably notablein the end parts in the width direction of the film. If the shrinkagedegree at the times of boiling treatment is lowered, the boiling strainis diminished. To lower the shrinkage degree, besides the stretchingstress is lowered by multilayer formation, which is a point of theinvention, the stretching conditions are also important. However, if theconditions are not considerably out of conventional conditions forstretching a polyamide resin, it can be sufficiently lowered. If theboiling strain exceeds 2.0%, curling is notable and therefore, it is notpreferable.

(Film Characteristics—Haze)

The haze of the biaxially stretched multilayer polyamide resin film inthe invention is preferably in a range of 1.0 to 20%. If the haze at thetime of stretching is 1.0% or lower, stable production becomes difficultand therefore, it is not preferable. If haze exceeds 20%, it becomesdifficult to see contents at the time of use and additionally, thedesign property is deteriorated and therefore, it is not preferable.

The haze of the system containing the layered compound of the inventionis the total derived from the resin, the inorganic layered compound, andvoids formed by separation of the resin from the inorganic layeredcompound surface at the time of stretching. It is preferable to decreasehaze specifically derived from the voids and for that, the stretchingconditions are preferably carefully set. When the MD temperature is toolow, the haze is increased due to void formation and therefore, it isnot preferable. Also, when the TD temperature is too high, haze increaseis observed due to crystallization and therefore, it is not preferable.A preferable temperature range is as described above and it can beadjusted with reference to these facts. Further, the haze can beadjusted in accordance with the size and type of the layered compound.For example, not only use of the layered compound with a size smallerthan the wavelength of visible light makes the haze small but also useof the layered compound with a refractive index close to that of theresin makes the haze small.

(Film Characteristics—Pinhole Resistance)

The biaxially stretched multilayer polyamide resin film in the inventionhas excellent pinhole resistance, and the number of pinholes after 1000times Gelbo Flex test at 23° C. is preferably 0 to 30. The pinholeresistance is mainly affected by the stretching conditions andparticularly, it is preferable that the temperature at the time of TDstretching is increased not so high. In the case the TD stretchingproperty is inferior, it is sometimes required to increase thetemperature. However, if the stretching temperature is increased toohigh beyond the low temperature crystallization temperature, partialcrystallization is promoted without progression of sufficient stretchingand thickness unevenness and pinholes tend to be formed easily in fineregions. Also, pinholes can easily form in the obtained film.

With respect to the TD stretching temperature, concretely, it ispreferably 155° C. or lower. If the TD stretching temperature exceeds155° C., the film tends to become brittle and the pinhole resistance isworsened.

(Film Characteristics—Equilibrium Moisture Content)

The equilibrium moisture content of the polyamide resin film in theinvention is preferably in a range of 3.5 to 10%. The equilibriummoisture content of a common biaxially stretched film of a polyamideresin is about 3% and the film of the invention is preferably higherthan that. Among commonly known layered compounds, most commonly usedmontmorillonite and smectite are generally used as a thickener forincreasing the viscosity of an aqueous solution. As being assumed fromthat, they have characteristics of taking water in inter-layers, beingswollen easily, and absorbing a large quantity of water. If thesecompounds are merely added to a resin, montmorillonite absorbs a largequantity of water. Therefore, the equilibrium moisture content in theresin composition becomes higher and the characteristics become highlymoisture-dependent. According to the invention, since the layeredcompound is highly in-plane orientated, and also, even if the additionamount is so high as to give the equilibrium moisture content of 3.5% orhigher, the moisture-dependency of the characteristics can be suppressedby biaxial stretching of the matrix polyamide resin at a high ratio andfurther carrying out orientation crystallization. If the equilibriummoisture content is less than 3.5%, the effect of the layered compoundaddition is slight and if it exceeds 10%, the addition amount is excessand preferable characteristics cannot be obtained.

(Film Characteristics—Gas Barrier Property)

In the invention, the multilayer film containing the layered compound isexcellent in the barrier property since the layered compound is orientedin the plane. It is preferable that the oxygen permeability inconversion into 15 μm is in a range of 5 to 20 cc/m²/day/atm. The upperlimit of the oxygen permeability is preferably 19 cc/m²/day/atm or lowerand more preferably 18 cc/m²/day/atm or lower. The oxygen barrierproperty depends on the in-plane orientation degree of the layeredcompound in the polyamide resin and the addition amount. A preferableaddition amount of the layered compound in terms of the oxygen barrierproperty is in a range of 0.3 to 10 wt. % with respect to the entirefilm. If the addition amount is less than 0.3 wt. %, the effect of thebarrier property is slight. If the addition amount exceeds 10 wt. %, thebalance with the characteristics such as the boiling strain is worsenedand therefore, it is not preferable. Further, aiming to further increasethe gas barrier property, it is preferable to add a resin with a highbarrier property and to laminate a resin layer with a high barrierproperty. Examples of the resin with a high barrier property arem-xylylenediamine type nylon (MXD6), polyvinyl alcohol, polyglycolicacid, etc. The addition amount and the laminating amount of thesecompounds is preferably 1 to 20%. If it is less than 1%, the effect ofimproving the barrier property is slight and if it exceeds 20%, theadded barrier resin and the stretching property cannot be well balancedand therefore, it is not preferable.

(Film Characteristics—Heat Shrinkage Ratio)

The biaxially stretched multilayer polyamide resin film of the inventionis preferable to have a heat shrinkage ratio at 160° C. for 10 minutesin a range of −0.5 to 1.5% in both the lengthwise direction andtransverse direction. In order to make the heat shrinkage ratio close tozero, it is preferable to optimize the stretching conditions, thermalfixation condition, and the thickness of the layer. For improvement ofthe stretching property, it is advantageous that the thickness of eachlayer is thin. However, if the layer is too thin, the heat shrinkageratio cannot be lowered by thermal fixation and therefore, the layerstructure is preferable to be determined in accordance with the aimedheat shrinkage ratio. To simultaneously provide both the desired heatshrinkage ratio and stretching property, the thickness of each layerbefore stretching is preferably in a range of 1 to 30 μm, and morepreferably in a range of 2 to 20 μm. The lower limit of the heatshrinkage ratio is more preferably 0% or higher and even more preferably0.1% or higher. The upper limit is preferably 1.5% or lower and morepreferably 1.3% or lower.

The biaxially stretched multilayer polyamide resin film of the inventionmay be subjected to corona treatment, coating treatment, or flametreatment to improve the adhesiveness and wettability in accordance withuse. With respect to the coating treatment, an in-line coating method ofstretching a coated product during film formation is preferably used.The biaxially stretched multilayer polyamide resin film of the inventionis generally further processed by printing, deposition, lamination, etc.in accordance with the desired end use.

The biaxially stretched polyamide resin film of the invention mayoptionally contain a hydrolysis resistant improver, an antioxidant, acoloring agent (a pigment, a dye), an antistatic agent, a conductiveagent, a flame retardant, a reinforcing agent, a filler, an inorganiclubricant, an organic lubricant, a nucleating agent, a release agent, aplasticizer, an adhesive aid, a pressure-sensitive adhesive, etc.

EXAMPLES

Next, the invention will be described more in detail with reference toExamples; however the invention is not to be considered as being limitedby these Examples, but is only limited by the scope of the appendedclaims. Measurement methods employed in the invention will be describedbelow.

(1) Haze

Haze was measured at different 3 points of each sample by using a hazemeter (NDH 2000, produced by Nippon Denshoku Industries Co., Ltd.)according to a method of JIS K7105 and the average value was employed.

(2) Measurement of Glass Transition Temperature (Tg) and Measurement ofLow Temperature Crystallization Temperature (Tc)

An un-oriented polyamide resin sheet was frozen in liquefied nitrogenand after thawing under reduced pressure, these temperatures weremeasured at a heating rate of 20° C./min by using DSC produced by SeikoInstruments Inc.

(3) Addition Amount of Inorganic Material Including Layered Compound(Residue Weight)

The weight of residue was measured by using TGA manufactured by TAInstruments after 0.1 g of each sample was heated to 500° C. at aheating rate of 20° C./min under nitrogen flow.

(4) Surface Roughness (Sa)

Small pieces of film were cut off from 3 arbitrary parts of each filmand dust or the like was carefully removed by a static eliminationblower. The heat adhesion layer surface of each piece was measured by anon-contact three-dimensional shape measurement apparatus (Micromap 557manufactured by Micromap Corp.). For the optical system, a Millot typetwo beam interference object lens (10 magnification) and a zoom lens(Body Tube; 0.5 magnification) were used. Light was received by a ⅔ inchCCD camera using a light source of 5600 angstrom. The measurement wascarried out in WAVE mode, and the visual field of 1619 μm×1232 μm wasprocessed as a digital image of 640×480 pixels. The image analysis wascarried out using an analysis software (Micromap 123, version 4.0) bydetrending in a linear function mode. Accordingly, arithmetic averagesurface roughness for 5 visible fields of each front face and each rearface of three samples (total 30 visible fields) were measured and theaverage value was defined as the surface roughness (Sa).

(5) Static Friction Coefficient

The static friction coefficient was measured by a friction coefficienttest method described in JIS K7125. Ten samples were cut off from 5arbitrary points of each film, and both front and rear faces of the filmwere set face to face for measurement. The normal stress calculated bythe load applied to the sliding specimen was set to be 0.5 N/cm², andthe average value of 5 times measurement results was defined as thestatic friction coefficient. The measurement environments were 23° C.and 65% RH.

(6) Gloss

As the gloss, 85-degree mirror face gloss was measured using a specimenof a size of 100×100 mm according to JIS K8741 with a gloss meter (glossmeter model 1001 DP, produced by Nippon Denshoku Industries Co., Ltd.).The value was the average value of front and rear faces.

(7) Mechanical Characteristic (Elastic Modulus)

The elastic modulus was measured according to JIS K 7113. Specimens witha width of 10 mm and a length of 100 mm in the width direction and thelongitudinal direction were cut off from each film by a razor and used.After the specimens were left in an atmosphere of 23° C. and 35% RH for12 hours, the measurement was carried out in an atmosphere of 23° C. and35% RH and under conditions of chuck interval of 40 mm and tensile speedof 200 mm/min. The average value of 5 times measurement results wasemployed. Autograph AG 5000 A manufactured by Shimadzu Corp. was used asa measurement apparatus. The high temperature MD elastic modulus wasmeasured in an oven heated to a prescribed temperature under conditionsof chuck interval of 40 mm and tensile speed of 200 mm/min. The averagevalue of 5 times measurement results was employed.

(8) Dynamic Viscoelasticity Test

The dynamic viscoelasticity measurement was determined by an apparatusproduced by I.T. Research Co., Ltd. under conditions of measurementlength of 30 mm, displacement of 0.25%, frequency of 10 Hz, and ameasurement environment temperature of 23° C. Each sample was cut off ina size of length 40 mm×width 5 mm in parallel to the width direction ofeach film. The average value of two points was employed. Calculation oftan δ was carried out according to the following expression:tan δ=(imaginary number of complex elastic modulus)/(real number ofcomplex elastic modulus).(9) Pinhole Resistance (Flex Resistant Fatigue Test)

Flex resistant fatigue property was measured by the following methodusing a Gelbo Flex tester produced by Rigaku Kogyo Co., Ltd. At first,each obtained film sample was attached in cylindrical form to a fixedhead with a diameter of 8.89 cm (3.5 inch) and a movable head with thesame diameter and arranged in parallel at an interval of 17.78 cm (7inch) from the fixed head. The movement of the movable head wascontrolled by a shaft installed in the center of the movable head. Atfirst, while being twisted at 440°, the movable head was moved closer by8.89 cm (3.5 inch) to the fixed head and next further moved closer by6.35 cm (2.5 inch) by horizontal movement and thereafter, the movablehead was turned back to the former state by the inversion movement. Thiscycle was repeated 1000 times at 23° C., 60% RH, and a speed of 40times/min. After repeating the cycle 1000 times, the number of pinholeswas measured. The measurement of the number was carried out by thefollowing method. The film was put on a filter paper (No. 50, Advantec)and four corners were fixed by SELLOTAPE™. Ink (produced by PilotCorporation (product No. INK-350-Blue) diluted fivefold with pure water)was applied to the test film and spread on one face by a rubber roller.After excess ink was wiped off, the test film was removed and the numberof points of the ink on the filter paper was counted.

(10) Mechanical Characteristics (Maximum Point Stress, BreakingElongation)

The maximum stress point and breaking elongation were measured accordingto JIS K 7113. Specimens with a width of 10 mm and a length of 100 mm inthe width direction and the longitudinal direction were cut off fromeach film by a razor and used. After the specimens were left in anatmosphere of 23° C. and 35% RH for 12 hours, the measurement wascarried out in an atmosphere of 23° C. and 35% RH and under conditionsof chuck interval of 40 mm and tensile speed of 200 mm/min. The averagevalue of 5 times measurement results was employed. Autograph AG 5000 Amanufactured by Shimadzu Corp. was used as a measurement apparatus.

(11) Relative Viscosity

The relative viscosity was measured at 20° C. after 0.25 g of nylonresin was dissolved in 25 ml of 96% sulfuric acid solution.

(12) In-Plane Orientation of Layered Compound

With respect to a film obtained by stretching a nylon 6 resin in whichmontmorillonite was dispersed, the in-plane orientation ofmontmorillonite was measured. In the case of compounds other thanmontmorillonite, measurement could be carried out in the same manner.RINT 2500 Cu-Kα produced by Rigaku Corporation was used as the apparatusand the half width of the peak of (060) montmorillonite was measured byx-ray diffractometry with output of 40 kV and 200 mA. The in-planeorientation of the inorganic layered compound was calculated from thehalf width according toin-plane orientation=(180−half width)/180.Herein, the half width of the peak of (060) of montmorillonite wasmeasured by the following method: (1) x-ray was led in the width (TD)direction to the film sample; (2) the sample was fixed at a position ofθ=31.4° to the incident x-ray and the detector was fixed at a positionof 2θ=62.8°; (3) x-ray diffraction intensity was measured by in-planerotating (β-rotation) the sample stage form 0 to 360′; (4) the portionformed by removing the surrounding of ±60° of the peak top from theobtained x-ray diffraction intensity plot (see FIGURE, which is an x-raydiffraction intensity plot of the film prepared in Example 8) wascollinearly approximated by a least-square method to obtain a base line;and (5) the peak width at the half height from the base line measured in(4) to the peak top was defined as the half width.(13) Observation of the Orientation State of Layered Compound in Film

Each sample was prepared by the following method and observed by atransmission electron microscope. At first, each sample film wasembedded in an epoxy resin. The epoxy resin employed was obtained bymixing Luveak 812, Luveak NMA (produced by Nacalai Tesque, Inc.), andDMP 30 (produced by TAAB Laboratories Equipment Ltd.) at a weight ratioof 100:89:3. After the sample film was embedded in the epoxy resin, itwas left for 16 hours in an oven controlled at a temperature of 60° C.to harden the epoxy resin and obtain an embedded block.

The embedded block was attached to Ultra-cut N produced by Nissei SangyoCorporation and ultrathin specimens were produced. At first, eachspecimen was trimmed until the cross section of the portion of the filmto be observed was exposed to the resin surface by a glass knife. Next,each ultra-thin specimen was cut off by a diamond knife (Sumi KnifeSK2045, produced by Sumitomo Electric Industries Ltd.). After the cutoff ultra-thin specimen was recovered on a mesh, thin carbon vapordeposition was carried out. An electron microscope observation wascarried out using JEM-2010 produced by JEOL Ltd. under condition ofaccelerating voltage of 200 kV. The image of the cross section of thefilm obtained by the electron microscopy was recorded on an imagingplate (FDLUR-V, produced by Fujifilm Corporation). From the image, 50layered compounds were extracted at random and the inclination of therespective compounds was evaluated.

In the case the inclination dispersion of the layered compound waswithin an angle of 20° or less, it was defined the layered compound wasin-plane orientated. Those in-plane orientated were marked with ∘ andthose which were not in-plane orientated were marked with x.

(14) Thickness and Number of Total Layers in Film

Each film was cooled by liquefied nitrogen and cut off in the widthdirection of the cast film or stretched film by a Feather blade toobtain a cross section immediately after taken out. The cross sectionwas observed by an optical microscope (BX 60, produced by OlympusCorporation) and the thickness of a layer was calculated by dividing thethickness of 5 to 20 layers by the number of the layers. The number ofthe total layers was measured by the same method.

In the case the interface of layers was difficult to distinguish in theabove-mentioned method, each sample was produced by the following methodand observed by a transmission electron microscope. At first, eachsample film was embedded in an epoxy resin. The epoxy resin employed wasobtained by mixing Luveak 812, Luveak NMA (produced by Nacalai Tesque,Inc.), and DMP 30 (produced by TAAB Laboratories Equipment Ltd) at aweight ratio of 100:89:3. After the sample film was embedded in theepoxy resin, it was left for 16 hours in an oven controlled at atemperature of 60° C. to harden the epoxy resin and obtain an embeddedblock. The embedded block was attached to Ultra-cut N produced by NisseiSangyo Corporation and ultrathin specimens were produced. At first, eachspecimen was trimmed until the cross section of the portion of the filmto be observed was exposed to the resin surface by a glass knife. Next,each ultra-thin specimen was cut off by a diamond knife (Sumi KnifeSK2045, produced by Sumitomo Electric Industries Ltd.). After the cutoff ultra-thin specimen was recovered on a mesh, thin carbon vapordeposition was carried out.

An electron microscope observation was carried out using JEM-2010produced by JEOL Ltd. under condition of accelerating voltage of 200 kV.The image of the cross section of the film obtained by the electronmicroscopy was recorded on an imaging plate (FDLUR-V, produced byFujifilm Corporation). From the image, the thickness of the layer havingthe maximum thickness thicker than the interval between interfaces ofthe respective layers was measured.

(15) Oxygen Permeability (OTR)

Oxygen permeability was measured at a humidity of 65% and a temperatureof 23° C. using an oxygen permeability measurement apparatus (OX-TRAN10/50A, produced by Modern Controls, Inc.). The obtained result wasconverted into a value with a thickness of 15 μm and the value wasdefined as the oxygen permeability (OTR, cc/m²/day/atm). The conversioninto the value with a thickness of 15 μm was done according to thefollowing:(OTR converted into value with a thickness of 15 μm)=(measuredOTR)×(film thickness,μm)/15(μm).(16) Piercing Strength

According to regulation of Food Sanitation Law, each sample was fixed ina cylindrical tool and a needle with a diameter of 1.0 mm and asemicircular tip end shape with a radius of 0.5 mm was thrust into thesample at a speed of 50 mm/min and the maximum load (N) until the needlepenetrated the sample was measured.

(17) Equilibrium Moisture Content

Each sample with a size of 10 cm square was dried at 60° C. for 24 hoursin a vacuum, and the weight (a) was measured. Thereafter, the sample wasleft in an environment of 40° C. and 90% RH for 12 hours, and the weight(b) was measured. The equilibrium moisture content was calculatedaccording the following expression.Equilibrium moisture content(%)=(b−a)/a×100.(18) Cleavage Resistance

Each film after biaxial stretching was cut out by a cutter, andSELLOTAPE™ was stuck to the end face and left at room temperature for 24hours. Thereafter, the tape was peeled at an angle of 90° and existenceof cleavage was confirmed.

(19) Boiling Strain

Each sample was cut in a square shape with each side of 21 cm and eachsample was left in environments of 23° C. and 65% RH for 2 hours orlonger. The length of two diagonal lines of each sample was measured anddefined as the length before treatment. Next, the sample was heated inboiling water for 30 minutes and taken out and thereafter wiped toremove the water adhering to the surface, dried by air blow, and left inan environment of 23° C. and 65% RH for 2 hours or longer. Then, thelength of two diagonal lines of the sample was measured again anddefined as the length after treatment. The shrinkage ratios in boilingwater in 45° direction and in 135° direction were calculated from themeasured values according to the following expression and the absolutevalue (%) of the difference was defined as the boiling strain. Theaverage value of hygroscopic difference of each sample was calculated.Shrinkage ratio in boiling water=[(length before treatment−length aftertreatment)/length before treatment]×100(%)(20) Heat Shrinkage Ratio

The measurement was carried out according to a dimensional change testmethod described in JIS C2318, except that the test temperature wasadjusted at 160° C. and the heating time was adjusted to 10 minutes.

At first, the first invention will be described with reference toExamples and Comparative Examples.

Example 1

After pellets of a nylon 6 resin (T-800, produced by Toyobo Co., Ltd.:relative viscosity RV=2.5, containing no lubricant) and pellets of anylon 6 resin containing montmorillonite as a layered compound dispersedevenly therein (NF 3040, produced by Nanopolymer Composite Corp.;addition amount of the layered compound: 4% (inorganic material 2.6%))were respectively vacuum-dried overnight at 100° C., they were blendedat a weight ratio of 1/1. Next, the blended pellets were supplied to twoextruders. After the pellets melted at 270° C. and the same kind resinwas laminated by a static mixer having 16 elements at 275° C., and thelaminate was extruded in a sheet-like form out of a T die heated at 270°C. to cooling rolls adjusted at 20° C. Next, the extruded sheet wascooled and hardened to obtain an un-stretched multilayer sheet. Theratio of the discharge amounts of the two extruders was controlled to be1:1. The thickness of the un-stretched sheet was 180 μm and thethickness of each layer in the center part in the width direction wasabout 1 μm. Tg of the sheet was 35° C. and the melting point was 225° C.The sheet was at first preheated at 65° C., stretched 2.5 times by MDstretching at a stretching temperature of 65° C. and a deformation speedof 16000%/min. Next, the sheet was continuously led to a tenter andstretched 3.8 times by TD stretching in a preheat zone at 65° C. and astretching zone at 135° C., subjected to thermal fixation at 210 and 5%transverse relaxation treatment. Thereafter, the sheet was cooled, andboth rim parts were cut and removed to obtain a biaxially stretchedpolyamide resin film with a thickness of 12 μm. The film had a width of40 cm and a length of 1000 m and was rolled around a paper tube. Thephysical properties of the film are shown in Table 1.

Examples 2 to 5, Example 7, Comparative Examples 1, 2, and ComparativeExamples 4 to 6

The samples were produced under the conditions described in Table 1. Thefilm properties of Examples are shown in Table 1, and the filmproperties of Comparative Examples are shown in Table 2.

Example 3 and Comparative Example 1 were made to be a monolayer withoutusing a static mixer. In Examples 4 and 5, TD stretching was carried outafter two-step MD stretching.

Example 6

After pellets of nylon 6 resin containing montmorillonite as a layeredcompound dispersed evenly therein (NF 3040, produced by NanopolymerComposite Corp.; addition amount of the layered compound: 4% (inorganicmaterial 2.6%)) and organically treated montmorillonite powder(CLOISITE™ 30B, produced by Southern Clay Products Inc.) wererespectively vacuum-dried overnight at 100° C., they were blended at aweight ratio to give the addition amount of the inorganic layeredcompound of 8%. Thereafter, the blended pellets were supplied to twoextruders and melted and mixed at 275° C. The obtained resin pelletswere again dried in a vacuum drier at 100° C. for 24 hours. The resinwas supplied to an extruder and melted at 275° C. and the same kind ofresin was laminated by a static mixer having 16 elements at 275° C., andthe laminate was extruded in a sheet-like form out of a T die heated at270° C. to cooling rolls adjusted at 20° C. and then cooled and hardenedto obtain an un-stretched multilayer sheet. The thickness of theun-stretched sheet was 180 μm, and the thickness of each layer in thecenter part in the width direction was about 1 μm. Tg of the sheet was35° C., and the melting point was 225° C. The sheet was at firstpreheated at 45° C., stretched 3.2 times by MD stretching by rolls witha surface temperature of 85° C. and a deformation speed of 4500%/min.Next, the sheet was continuously led to a tenter and stretched 3.8 timesby TD stretching in a preheat zone at 110° C. and a stretching zone at130° C., subjected to thermal fixation at 210° C. and 5% transverserelaxation treatment. Next, the sheet was cooled, and both rim partswere cut and removed to obtain a biaxially stretched polyamide resinfilm with a thickness of 15 μm. The physical properties of the film areshown in Table 1.

Comparative Example 3

After pellets of a nylon 6 resin (T-800, produced by Toyobo Co., Ltd.:relative viscosity RV=2.5, containing no lubricant) and silica particlesas a lubricant (SILYSIA™ 310, produced by Fuji Silysia Chemical Ltd.)were respectively vacuum-dried overnight at 100° C., they were mixed byan extruder at 270° C. and melted and mixed at 275 to give the lubricantconcentration of 1000 ppm. The obtained resin pellets were again driedin a vacuum drier at 100° C. for 24 hours. The resin was supplied to anextruder and melted at 275° C. and the same kind of resin was laminatedby a static mixer having 16 elements at 275° C. and the laminate wasextruded in a sheet-like form out of a T die heated at 270° C. tocooling rolls adjusted at 20° C. and then cooled and hardened to obtainan un-stretched multilayer sheet. The thickness of the un-stretchedsheet was 180 μm, and the thickness of each layer in the center part inthe width direction was about 1 μm. Tg of the sheet was 35° C., and themelting point was 225° C. The sheet was at first preheated at 45° C.,stretched 3.2 times by MD stretching by rolls with a surface temperatureof 60° C. and a deformation speed of 16000%/min. Next, the sheet wascontinuously led to a tenter and stretched 3.8 times by TD stretching ina preheat zone at 110° C. and a stretching zone at 130° C., subjected tothermal fixation at 210° C. and 5% transverse relaxation treatment.Next, the sheet was cooled, and both rim parts were cut and removed toobtain a biaxially stretched polyamide resin film with a thickness of 15μm. The physical properties of the film are shown in Table 2.

TABLE 1 Examples 1 2 3 4 5 6 7 Cast Resin 1 NF3040/ NF3040 NF3040 NF3040NF3040 NF3040 + NF3040 + T800 Cloisite T800 Melting temperature 270 270275 285 290 275 270 (° C.) Resin 2 NF3040/ NF3040 — NF3040 NF3040NF3040 + NF3040 + T800 Cloisite T800 Melting temperature 270 270 — 285290 275 270 (° C.) Layer ratio 50/50 50/50 — 50/50 45/55 50/50 50/50Laminate portion 270 275 275 275 280 275 270 temperature (° C.) Addingamount of 2 4 4 4 4 8 1.5 layerd compound (%) Content of inorganic 1.32.6 2.6 2.6 2.6 5.2 1.0 material (%) Number of layers 100 or more 100 ormore 1 100 or more 100 or more 100 or more 100 or more MD Preheating 6545 40 45 45 45 45 streching temperature (° C.) Streching 65 85 70 80 8085 75 temperature (° C.) Ratio (times) 2.5 3.2 3.2 2.0, 2.0 1.5, 2.3 3.23.2 Deformation speed 16000 4500 900 1950, 1950 1200, 2700 4500 4500(%/min) Ny(A)-Ny(B) 0.006 0.003 0.002 0.004 0.002 0.003 0.003 TDPreheating temperature (° C.) 65 110 110 110 110 110 110 strechingStreching temperature (° C.) 135 130 130 135 135 130 100 Ratio (times)3.8 3.8 3.8 3 4 3.8 3.8 Thermal Temperature (° C.) 210 210 210 210 210210 210 fixation Relaxation Temperature (° C.) 210 210 210 210 210 210210 Relaxation ratio (%) 3 5 5 5 5 5 5 Properties Thickness (μm) 12 2020 15 13 15 15 The in-plane orientation ◯ ◯ ◯ ◯ ◯ ◯ ◯ state of layeredcompound Haze (%) 5 8 13 9 8 17 1.5 MD elastic modulus (GPa) 2.9 2.5 1.92.1 1.9 3.4 1.8 Surface roughness (Sa) 0.0154 0.0128 0.03 0.025 0.0240.097 0.032 Static friction coefficient μs 0.93 0.79 0.78 0.82 0.80 0.400.95 The number of pinholes 9 2 12 1 1 16 20 85-degree gloss 82 78 80 6569 64 74 In-plane orientation of 0.73 0.82 0.8 0.79 0.84 0.75 0.71layered compound Two numerical values described in one cell indicate thedata on the first and second steps of the two-steps lengthwisestrecthing in this order

TABLE 2 Comparative Examples 1 2 3 4 5 6 Cast Resin 1 NF3040 NF3040 +T800 T800 NF3040 + NF3040 T800 T800 Melting temperature (° C.) 275 270270 270 275 280 Resin 2 — NF3040 + T800 T800 NF3040 + NF3040 T800 T800Melting temperature (° C.) — 270 270 270 275 280 Layer ratio — 50/5050/50 50/50 50/50 50/50 Laminate portion 270 270 270 270 270 285temperature (° C.) Adding amount of layerd 4 0.5 0 0 2 4 compound (%)Content of inorganic 2.6 0.8 0.1 0 1.3 2.6 material (%) Number of layers1 100 or more 100 or more 100 or more 100 or more 100 or more MDPreheating temperature (° C.) 45 60 60 60 40 60 streching Strechingtemperature (° C.) 80 60 60 60 70 80 Ratio (times) 3.2 3.2 3.2 2 2.5 3.2Deformation speed (%/min) 4500 16000 16000 4500 4500 4500 Ny(A)-Ny(B)0.0008 0.008 0.008 0.008 0.0057 0.008 TD Preheating temperature (° C.)110 60 60 60 65 60 streching Streching temperature 130 135 135 135 135175 (° C.) Ratio (times) 3.8 3.8 3.8 4 2 3.8 Thermal Temperature (° C.)210 210 210 210 210 210 fixation Relaxation Temperature (° C.) 210 210210 210 210 210 Relaxation ratio (%) 5 3 3 3 3 3 Properties Thickness(μm) 20 15 15 13 15 14 The in-plane orientation ◯ ◯ — — X ◯ state oflayered compound Haze (%) 25 5 12 9 6 39 MD elastic modulus (GPa) 2.61.6 1.5 1.9 1.2 2.2 Surface roughness (Sa) 0.06 0.02 0.12 0.05 0.03 0.05Static friction coefficient μs 0.9 1.5 0.8 1.9 1.1 1.3 The number ofpinholes 18 5 2 12 17 35 85-degree gloss 51 70 49 44 54 45 In-planeorientation of 0.55 0.4 — — 0.2 0.52 layered compound

Comparative Example 7

After pellets of nylon 6 resin containing montmorillonite as a layeredcompound dispersed evenly therein (NF 3040, produced by NanopolymerComposite Corp.; addition amount of the layered compound: 4% (inorganicmaterial 2.6%)) were vacuum-dried overnight at 100° C., the same resinwas supplied to two extruders, melted at 280° C., and laminated by astatic mixer having 16 elements heated at 280° C. The laminate wasextruded in a sheet-like form out of a T die heated at 275° C. tocooling rolls adjusted at 20° C. and then cooled and hardened to obtainan un-stretched multilayer sheet. The ratio of the discharge amounts ofthe two extruders was controlled to be 1:1. The thickness of theun-stretched sheet was 150 μm, the thickness of each layer measured in across section was about 1 μm, and the number of the layers was 100 orhigher. The Tg of the sheet was 35° C., and the melting point was 225°C. The sheet was at first preheated at 40° C., stretched 2 times byvertical stretching at a stretching temperature of 60° C. and adeformation speed of 2300%/min, and successively the sheet wascontinuously led to a tenter and stretched 2 times by transversestretching at a preheating temperature of 60° C. and stretchingtemperature of 70° C. Next, the film was subjected to thermal fixationat 210° C. and 5% transverse relaxation treatment, and thereafter,cooled. The un-stretched part in the width direction was cut and removedto obtain a biaxially stretched polyamide resin film with a thickness of30 μm. The film had a width of 40 cm and a length of 1000 m and wasrolled around a paper tube. The physical properties at that time areshown in Table 4.

Example 8

An un-stretched sheet was obtained in the same manner as ComparativeExample 7. Next, the un-stretched sheet was preheated by rolls with asurface temperature of 45° C. and stretched 3.2 times by lengthwisestretching using rolls with a surface temperature of 80° C. and adeformation speed of 4500%/min. Next, the sheet was continuously led toa tenter and stretched 3.8 times by transverse stretching at apreheating temperature of 110° C. and a stretching temperature of 135°C. and subjected to thermal fixation at 210° C. and 5% transverserelaxation treatment. Thereafter, the film was cooled, and both rimparts were cut and removed to obtain a biaxially stretched polyamideresin film with a thickness of 12 μm. The film had a width of 40 cm anda length of 1000 m and was rolled around a paper tube. The physicalproperties at that time are shown in Table 3. The in-plane orientationof the layered compound was improved from 0.2, which was the in-planeorientation of Comparative Example 7, to 0.82, and the OTR value inconversion into 15 μm was remarkably lowered from 17 cc to 12 cc.

Example 9

After pellets of nylon 6 resin containing montmorillonite as a layeredcompound dispersed evenly therein (NF 3040, produced by NanopolymerComposite Corp.; addition amount of the layered compound: 4% (inorganicmaterial 2.6%)) were vacuum-dried overnight at 100° C., the pellets weresupplied to an extruder and melted at 290° C. After the resintemperature was adjusted at 270° in a melt-line, the melted resin wasintroduced into a static mixer with 16 elements heated at inlet part of270° C. and at center to outlet part of 285° C. and the same kind ofresin was laminated. The laminate was extruded in a sheet-like form outof a T die heated at 280° C. to cooling rolls adjusted at 20° C. andthen cooled and hardened to produce an un-stretched multilayer sheet.The thickness of the un-stretched sheet was 200 μm, and the thickness ofeach layer in the center part in the width direction was about 1 μm. TheTg of the sheet was 40° C. The sheet was at first preheated at 45° C.and stretched by two-step stretching at a stretching temperature of 80°C. The first MD stretching was carried out at 1950%/min 2 times and thesecond MD stretching was carried out also at 1950%/min 2 times. Next,the sheet was continuously led to a tenter and stretched 4 times by TDstretching in a preheat zone at 110° C. and a stretching zone at 130°C., subjected to thermal fixation at 210 to 215° C. and 5% transverserelaxation treatment. Thereafter, the film was cooled, and both rimparts were cut and removed to obtain a biaxially stretched polyamideresin film with a thickness of 15 μm. The film had a width of 40 cm anda length of 1000 m and was rolled around a paper tube. The obtained filmhad excellent cleavage resistance. The physical properties of the filmare shown in Table 3. The in-plane orientation of the layered compoundwas improved from 0.2, which was the in-plane orientation of ComparativeExample 7, to 0.89, and the OTR value in conversion into 15 μm wasremarkably lowered from 17 cc to 10 cc.

Examples 10 to 12

The samples were produced under the conditions described in Table 3. Thefilm properties are shown in Table 3. Along with improvement of thein-plane orientation of the layered compound, the OTR value inconversion into 15 μm was improved to be around 12 cc.

Comparative Example 8

Pellets of nylon 6 resin containing montmorillonite as a layeredcompound dispersed evenly therein (NF 3040, produced by NanopolymerComposite Corp.; addition amount of the layered compound: 4% (inorganicmaterial 2.6%)) were vacuum-dried overnight at 100° C. Film formationwas carried out using a monolayer inflation film formation apparatus.The pellets were supplied to an extruder and melted at 290° C. Next, thefilm was extruded out of a circular die heated at 280° C. and cooledwith air and simultaneously, the discharge amount, rolling speed, andtube diameter were adjusted so as to control the stretching ratio of 4times on the basis of the area. The center part of the tube was cut toobtain a biaxially stretched polyamide resin film with a thickness of 20μm. The physical properties at that time are shown in Table 4.

Comparative Example 9

After pellets of poly(ethylene terephthalate) resin (RE 553, produced byToyobo Co., Ltd.) and a powder of montmorillonite (CLOISITE™ 10A,produced by Southern Clay Products Inc.) as a layered compound wererespectively vacuum-dried overnight at 100° C., they were dry-blended ata weight ratio of 85/15 and supplied to two extruders and melted andmixed at 295° C. The obtained resin pellets were again dried in a vacuumdrier at 100° C. for 24 hours. The resin was supplied to an extruder andmelted at 295° C. and the same kind of resin was laminated by a staticmixer having 16 elements at 285° C. The laminate was extruded in asheet-like form out of a T die heated at 285° C. to cooling rollsadjusted at 20° C. and then cooled and hardened to obtain anun-stretched multilayer sheet. The thickness of the un-stretched sheetwas 100 μm, and the thickness of each layer in the center part in thewidth direction was about 1 μm. The Tg of the sheet was 65° C. The sheetwas at first preheated at 90° C., stretched 2 times by MD stretching byrolls with a surface temperature of 110° C. and a deformation speed of2500%/min. Next, the sheet was continuously led to a tenter andstretched 2 times by TD stretching in a preheat zone at 90° C. and astretching zone at 100° C., subjected to thermal fixation at 230° C. and5% transverse relaxation treatment. Thereafter, the film was cooled, andboth rim parts were cut and removed to obtain a biaxially stretchedpoly(ethylene terephthalate) resin film with a thickness of 25 μm. Thefilm had a width of 40 cm and a length of 1000 m and was rolled around apaper tube. The physical properties of the film are shown in Table 4.

Reference Example 1

A biaxially stretched poly(ethylene terephthalate) resin film wasobtained in the same manner as Comparative Example 9, except that thethickness of the sheet before stretching was 400 μm, the MD stretchingratio was 4 times, and the TD stretching ratio was 4 times. The film hada width of 40 cm and a length of 1000 m and was rolled around a papertube. The physical properties of the film are shown in Table 3. Ascompared with Comparative Example 9, along with improvement of thein-plane orientation, the storage elastic modulus at 100° C. in thedynamic viscoelasticity of the obtained film was increased about doublefrom 20 MPa to 50 MPa and the heat resistance was improved.

Comparative Example 10

After pellets of polypropylene resin (Noblen FS2011, produced bySumitomo Chemical Co., Ltd.) and a powder of organically treatedmontmorillonite (CLOISITE™ 30B, produced by Southern Clay Products Inc.)as a layered compound were dry-blended at a weight ratio of 80/20 andsupplied to two extruders and melted and mixed at 270° C. The obtainedresin pellets were dried in a vacuum drier at 100° C. for 24 hours. Theresin was supplied to an extruder and melted at 275° C. and the samekind of resin was laminated by a static mixer having 16 elements at 275°C. The laminate was extruded in a sheet-like form out of a T die heatedat 275° C. to cooling rolls adjusted at 20° C. and then cooled andhardened to obtain an un-stretched multilayer sheet. The thickness ofthe un-stretched sheet was 150 μm, and the thickness of each layer inthe center part in the width direction was about 1 μm. The sheet was atfirst preheated at 50° C., stretched 2 times by MD stretching by rollswith a surface temperature of 130° and a deformation speed of 3000%/min.Next, the sheet was continuously led to a tenter and stretched 2 timesby TD stretching in a preheat zone at 160° C. and a stretching zone at165° C., subjected to thermal fixation at 155° C. and 5% transverserelaxation treatment. Thereafter, the film was cooled, and both rimparts were cut and removed to obtain a biaxially stretched polypropyleneresin film with a thickness of 25 μm. The film had a width of 40 cm anda length of 1000 m and was rolled around a paper tube. The physicalproperties of the film are shown in Table 4.

Reference Example 2

A biaxially stretched polypropylene resin film was obtained in the samemanner as Comparative Example 10, except that the thickness of the sheetbefore stretching was made to be 1000 μm, the MD stretching ratio was 6times, and the TD stretching ratio was 8 times. The film had a width of40 cm and a length of 1000 m and was rolled around a paper tube. Thephysical properties of the film are shown in Table 3. The in-planeorientation was sufficiently high and, for example, it was expected thatthe gas barrier property and heat resistance were improved.

Reference Example 3

After pellets of a MXD6 type polyamide resin containing montmorilloniteas a layered compound evenly dispersed therein (IMPERM™ 105, produced byNanocor, Inc., layered compound addition amount: 7%) were vacuum-driedovernight at 100° C., the pellets were supplied to an extruder andmelted at 280° C. A static mixer with 16 elements heated at 280° C. wasintroduced in a melt-line, and the same kind of resin was laminated. Thelaminate was extruded in a sheet-like form out of a T die heated at 270°C. to cooling rolls adjusted at 20° C. and then cooled and hardened toproduce an un-stretched multilayer sheet. The thickness of theun-stretched sheet was 200 μm, and the thickness of each layer in thecenter part in the width direction was about 1 μm. The sheet was atfirst preheated at 80° C. and stretched at a stretching temperature of100° C. and a deformation speed of 5000%/min and ratio of 3.5 times.Next, the sheet was continuously led to a tenter and stretched 3.5 timesby TD stretching in a preheat zone at 80° C. and a stretching zone at95° C., subjected to thermal fixation at 180° C. and 3% transverserelaxation treatment. Thereafter, the film was cooled, and both rimparts were cut and removed to obtain a biaxially stretched polyamideresin film with a thickness of 15 μm. The film had a width of 40 cm anda length of 1000 m and was rolled around a paper tube. The physicalproperties of the film are shown in Table 3.

TABLE 3 Examples Reference Examples 8 9 10 11 12 1 2 3 Cast Resin 1NF3040 NF3040 NF3040 NF3040 NF3040 + RE553 + FS2011 + Imperm 105Cloisite Cloisite 10A Cliisite Melting temperature 280 290 275 275 275295 275 280 (° C.) Resin 2 NF3040 NF3040 NF3040 NF3040 + NF3040 +RE553 + FS2011 + Imperm 105 T800 (50/50) Cloisite Cloisite 10A CliisiteMelting temperature (° C.) 280 290 275 285 275 295 275 280 Layer ratio50/50 50/50 50/50 70/30 50/50 50/50 50/50 50/50 Laminate portiontemperature 280 270/285 275 275 275 285 275 280 (° C.) Adding amount oflayerd 4 4 4 3.4 8 15 5 7 compound (%) Content of inorganic material 2.62.6 2.6 2.2 5.2 15 3.2 5 (%) Number of layers 100 or 100 or more 100 ormore 8 100 or 100 or more 100 or 100 or more more more more MDPreheating temperature 45 45 45 45 45 90 50 80 streching (° C.)Streching temperature 80 80 80 80 85 110 135 100 (° C.) Ratio (times)3.2 2.0, 2.0 3.2 3.2 3.2 4.0 6.0 3.5 Deformation speed (%/min) 45001950, 1950 16000 4500 4500 5000 9000 5000 TD Preheating temperature (°C.) 110 110 110 110 110 90 160 80 streching Streching temperature (° C.)135 130 130 135 130 100 165 95 Ratio (times) 3.8 4.0 3.8 3.0 3.8 4.0 8.03.5 Thermal Temperature (° C.) 210 210 210 210 210 230 155 180 fixationRelaxation Temperature (° C.) 210 210 210 210 210 230 155 180 Relaxationratio (%) 5 5 5 5 5 5 5 3 Properties Thickness (μm) 12 15 18 18 15 25 2515 The in-plane orientation ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ state of layered compoundHaze (%) 11 10 11 11 15 20 10 19 MD elastic modulus (GPa) 2.7 2.7 2.92.5 2.8 3.8 Surface roughness (Sa) 0.0124 0.0118 0.0140 0.0100 0.08000.062 Static friction coefficient μs 0.78 0.78 0.81 0.77 0.83 0.54 Thenumber of pinholes 2 1 2 1 14 18 In-plane orientation of 0.82 0.89 0.760.81 0.52 0.72 0.88 0.62 layered compound OTR (cc/m2/day/atm) 12 10 1212 7 25 — 1 High temperature MD 1.3 1.2 1.3 1.0 1.5 1.3 — 1.8 elasticmodulus (MPa) Measurement temperature 80 80 80 80 80 100 — 80 (° C.)

TABLE 4 Comparative Examples 7 8 9 10 Cast Resin 1 NF3040 NF3040 RE553 +FS2011 + Cloisite 10A Cloisite 30B Melting temperature (° C.) 280 275295 275 Resin 2 NF3040 — RE553 + NF3040 + Cloisite 10A Cloisite 30BMelting temperature (° C.) 280 — 295 275 Layer ratio 50/50 — 50/50 50/50Laminate portion temperature (° C.) 280 275 285 275 Adding amount oflayerd compound (%) 4 4 15 5 Content of inorganic material (%) 2.6 2.615 3.3 Number of layers 100 or more 1 100 or more 100 or more MDPreheating temperature (° C.) 40 — 90 50 streching Streching temperature(° C.) 60 — 110 130 Ratio (times) 2.0 2 2.0 2.0 Deformation speed(%/min) 4500 — 2500 3000 TD Preheating temperature (° C.) 60 — 90 160streching Streching temperature (° C.) 70 — 100 165 Ratio (times) 2.0 22.0 2.0 Thermal Temperature (° C.) 210 — 230 155 fixation RelaxationTemperature (° C.) 210 — 230 155 Relaxation ratio (%) 5 — 5 5 PropertiesThickness (μm) 30 20 25 25 The in-plane orientation state of x x x xlayered compound Haze (%) 13 8 30 17 MD elastic modulus (GPa) 1.2 0.8Surface roughness (Sa) 0.03 0.005 Static friction coefficient μs 1.1 1.8The number of pinholes 17 5 In-plane orientation of layered 0.2 0.1 orless 0.2 0.2 compound OTR (cc/m2/day/atm) 17 20 44 — High temperature MDelastic 0.7 0.6 0.8 — modulus (M Pa) Measurement temperature (° C.) 8080 100 — (Attention) Since Cloisite 10A does not containe organictreatment agent, adding amount of layerd compound is equal to content ofinorganic material

Example 13

After pellets of nylon 6 resin containing montmorillonite as a layeredcompound dispersed evenly therein (NF 3040, produced by NanopolymerComposite Corp.; addition amount of the layered compound: 4% (inorganicmaterial 2.6%)) were vacuum-dried overnight at 100° C., the pellets weresupplied to two extruders and melted at 285° C. and the same resin waslaminated by a static mixer having 10 elements heated at 285° C. Thelaminate was extruded in a sheet-like form out of a T die heated at 280°C. to cooling rolls adjusted at 20° C. and then cooled and hardened toobtain an un-stretched multilayer sheet. The ratio of the dischargeamounts of the two extruders was controlled to be 1:1. The thickness ofthe un-stretched sheet was 240 μm, and the thickness of each layer inthe center part in the width direction was about 1 μm. The Tg of thesheet was 35° C., and the melting point was 225° C. The sheet was atfirst preheated at 45° C., stretched 3.5 times by MD stretching atstretching temperature of 85° C. and a deformation speed of 4500%/min.Next, the sheet was continuously led to a tenter and stretched 3.8 timesby TD stretching in a preheat zone at 65° C. and a stretching zone at135° C., subjected to thermal fixation at 210° C. and 5% transverserelaxation treatment. Thereafter, the film was cooled, and both rimparts were cut and removed to obtain a biaxially stretched polyamideresin film with a thickness of 18 μm. The film had a width of 40 cm anda length of 1000 m and was rolled around a paper tube. The physicalproperties of the film are shown in Table 5.

Examples 14 to 18

The samples were produced under the conditions described in Table 5. InExamples 15, 17, and 18, TD stretching was carried out after two-step MDstretching. Each film had a width of 40 cm and a length of 1000 m andwas rolled around a paper tube. The physical properties of the films areshown in Table 5.

Reference Example 4

After pellets of nylon 6 resin containing montmorillonite as a layeredcompound dispersed evenly therein (NF 3040, produced by NanopolymerComposite Corp.; addition amount of the layered compound: 4% (inorganicmaterial 2.6%)) and organically treated montmorillonite powder(CLOISITE™ 30B, produced by Southern Clay Products Inc.) wererespectively vacuum-dried overnight at 100° C., they were dry-blended ata weight ratio of 92/8. Thereafter, the blended pellets were supplied totwo extruders and melted and mixed at 285° C. The obtained resin pelletswere again dried in a vacuum drier at 100° C. for 24 hours. The resinwas supplied to an extruder and melted at 285° C. and the same kind ofresin was laminated by a static mixer with 16 elements at 280° C. Thelaminate was extruded in a sheet-like form out of a T die heated at 270°C. to cooling rolls adjusted at 20° C. and then cooled and hardened toobtain an un-stretched multilayer sheet. The thickness of theun-stretched sheet was 180 μm, and the thickness of each layer in thecenter part in the width direction was about 1 μm. The Tg of the sheetwas 35° C., and the melting point was 225° C. The sheet was at firstpreheated at 45° C., stretched 3.0 times by MD stretching by rolls witha surface temperature of 85° C. and a deformation speed of 2000%/min.Next, the sheet was continuously led to a tenter and stretched 3.8 timesby TD stretching in a preheat zone at 110° C. and a stretching zone at135° C., subjected to thermal fixation at 210° C. and 5% transverserelaxation treatment. Thereafter, the film was cooled, and both rimparts were cut and removed to obtain a biaxially stretched polyamideresin film with a thickness of 15 μm. The film had a width of 40 cm anda length of 1000 m and was rolled around a paper tube. The physicalproperties of the film are shown in Table 5.

Comparative Example 11

Pellets of nylon 6 resin containing montmorillonite as a layeredcompound dispersed evenly therein (NF 3040, produced by NanopolymerComposite Corp.; addition amount of the layered compound: 4%) werevacuum-dried overnight at 100° C. Film formation was carried out using amonolayer inflation film formation apparatus. The pellets were suppliedto an extruder and melted at 275° C. Next, the film was extruded out ofa circular die heated at 275° C. and cooled with air. The dischargeamount, rolling speed, and tube diameter were adjusted so as to controlthe stretching ratio of 2 times on the basis of the area. The centerpart of the tube was cut to obtain a biaxially stretched polyamide resinfilm with a thickness of 15 μm. The physical properties at that time areshown in Table 6.

Comparative Examples 12 to 14

The samples were produced under the conditions described in Table 6. InExamples 12 and 14, no static mixer was used and the films were made tobe monolayer. Each film had a width of 40 cm and a length of 1000 m andwas rolled around a paper tube. The physical properties of the films areshown in Table 6.

TABLE 5 Reference Examples Example 13 14 15 16 17 18 4 Cast Resin 1NF3040 NF3040 + NF3040 NF3040 NF3040 NF3040 NF3040 + T800 (50/50)Cloisite 30B Melting temperature (° C.) 285 285 285 285 290 290 285Resin 2 NF3040 NF3040 + NF3040 T814 NF3040 NF3040 NF3040 + T800 (50/50)Cloisite 30B Melting temperature (° C.) 285 285 285 270 290 290 285Layer ratio 50/50 50/50 50/50 25/75 45/55 50/50 50/50 Laminate portion285 285 275 270 275 280 280 temperature (° C.) Adding amount of layerd 42 4 1 4 4 12 compound (%) Content of inorganic material 2.6 1.3 2.6 0.92.6 2.6 8 (%) Number of layers 100 or more 100 or more 100 or more 100or more 100 or more 100 or more 100 or more MD Preheating temperature (°C.) 45 65 45 60 45 45 45 streching Streching temperature (° C.) 85 85 7080 80 85 85 Ratio (times) 3.5 2.5 2.0 × 2.0 3.5 1.5 × 1.8 2.0 × 2.2 3.0Deformation speed (%/min) 4500 16000 1950 + 1950 4500 1200 + 2700 1950 +1950 2000 Ny(A)-Ny(B) 0.003 0.006 0.003 0.006 0.003 0.003 0.003 TDPreheating temperature (° C.) 65 110 110 70 110 110 110 strechingStreching temperature (° C.) 135 135 140 70 140 140 135 Ratio (times)3.8 3.8 4.0 3.8 4.0 4.0 3.8 Thermal Temperature (° C.) 210 210 210 210210 210 210 fixation Relaxation Temperature (° C.) 210 210 210 210 210210 210 Relaxation ratio (%) 5 3 5 5 5 5 5 Properties Thickness (μm) 1813 12 15 12 8 15 The in-plane orientation state ◯ ◯ ◯ ◯ ◯ ◯ ◯ of layeredcompound Haze (%) 11 5 13 3 10 16 17 MD elastic modulus (GPa) 2.5 2.42.9 2.5 2.5 2.9 2.8 Surface roughness (Sa) 0.0125 0.015 0.021 0.03000.018 0.0125 0.0800 Static friction coefficient μs 0.73 0.93 0.65 0.440.72 0.74 0.75 The number of pinholes 1 6 2 2 1 1 15 In-planeorientation of 0.81 0.70 0.86 0.64 0.59 0.85 0.52 layered compoundIn-plane orientation (ΔP) 0.060 0.059 0.065 0.065 0.057 0.063 0.057Piercing strength/thickness 1.1 0.9 1.3 0.9 1.3 1.8 0.9 (N/um) T800:Polyamide resin produced by Toyobo Co., Ltd.: RV = 2.5, containing nolubricant T814: Polyamide resin produced by Toyobo Co., Ltd.: RV = 2.5,silica content 3500 ppm

TABLE 6 Comparative Examples 11 12 13 14 Cast Resin 1 NF3040 T814 NF3040NF3040 Melting temperature (° C.) 275 270 275 275 Resin 2 — — NF3040 —Melting temperature (° C.) — — 275 — Layer ratio — — 50/50 — Laminateportion temperature (° C.) 275 270 270 270 Adding amount of layerdcompound (%) 4 0 4 4 Content of inorganic material (%) 2.6 0.35 2.6 2.6Number of layers 1 1 100 or more 1 MD Preheating temperature (° C.) — 6045 40 streching Streching temperature (° C.) — 60 80 70 Ratio (times)1.4 3.2 1.5 3 Deformation speed (%/min) — 4500 1500 4500 Ny(A)-Ny(B) —0.007 0.001 0.000 TD Preheating temperature (° C.) — 60 110 55 strechingStreching temperature (° C.) — 70 130 70 Ratio (times) 1.4 3.8 2.0 2.5Thermal Temperature (° C.) — 210 210 210 fixation Relaxation Temperature(° C.) — 210 210 210 Relaxation ratio (%) — 5 5 3 Properties Thickness(μm) 15 15 18 18 The in-plane orientation state of x — x x layeredcompound Haze (%) 9 3 10 11 MD elastic modulus (GPa) 0.8 1.5 0.9 0.8Surface roughness (Sa) 0.0050 0.1200 0.1500 0.0300 Static frictioncoefficient μs 1.8 0.8 1.1 1.2 The number of pinholes 5 2 25 14 In-planeorientation of layered 0.1 or less — 0.1 or less 0.33 compound In-planeorientation (ΔP) 0.003 0.06 0.055 0.056 Piercing strength/thickness(N/μm) 0.5 0.7 0.6 0.65

Example 19

After pellets of nylon 6 resin containing montmorillonite as a layeredcompound dispersed evenly therein (NF 3040, produced by NanopolymerComposite Corp.; addition amount of the layered compound: 4%) werevacuum-dried overnight at 100° C., the same resin was supplied to twoextruders and melted at 280° C. and laminated by a static mixer with 16elements at 280° C. The laminate was extruded in a sheet-like form outof a T die heated at 275° C. to cooling rolls adjusted at 20° C. andthen cooled and hardened to obtain an un-stretched multilayer sheet. Theratio of the discharge amounts of the two extruders was controlled to be1:1. The thickness of the un-stretched sheet was 180 μm, the thicknessof each layer was about 1 μm in the cross section, and the number of thelayers was 100 or more. The Tg of the sheet was 35° C., and the meltingpoint was 225° C. The sheet was at first preheated at 45° C., stretched3.2 times by lengthwise stretching at a stretching temperature of 85° C.and a deformation speed of 4500%/min. Next, the sheet was continuouslyled to a tenter and stretched 3.8 times by transverse stretching in apreheat zone at 110° C. and a stretching zone at 130° C., subjected tothermal fixation at 210° C. and 5% transverse relaxation treatment.Thereafter, the film was cooled, and the un-stretched part in the widthdirection was cut and removed to obtain a biaxially stretched polyamideresin film with a thickness of 18 μm. The film had a width of 40 cm anda length of 1000 m and was rolled around a paper tube. The physicalproperties of the film are shown in Table 7.

Examples 20 and 21 and Comparative Examples 16 to 18

The samples were produced in the same manner as Example 19 under theconditions described in Table 7. The film properties are shown in Table7. In Example 21, a multilayer sheet was produced by using a staticmixer with 6 elements. In Comparative Example 18, a sample was producedfrom a monolayer sheet by using a feed block with a monolayer structure.

Comparative Example 15

Pellets of nylon 6 resin containing montmorillonite as a layeredcompound dispersed evenly therein (NF 3040, produced by NanopolymerComposite Corp.; addition amount of the layered compound: 4%) werevacuum-dried overnight at 100° C. Film formation was carried out using amonolayer inflation film formation apparatus. The pellets were suppliedto an extruder and melted at 290° C. Next, the film was extruded out ofa circular die heated at 280° C. and cooled with air and simultaneously,the discharge amount, rolling speed, and tube diameter were adjusted soas to control the stretching ratio of 4 times on the basis of the area.The center part of the tube was cut to obtain a biaxially stretchedpolyamide resin film with a thickness of 15 μm. The film had a width of40 cm and a length of 1000 m and was rolled around a paper tube. Thephysical properties at that time are shown in Table 7.

TABLE 7 Examples Comparative Examples 19 20 21 15 16 17 18 Cast Resin 1NF3040 NF3040 NF3040 NF3040 T814 NF3040 + NF3040 + T814 T814 (50/50)(12.5/87.5) Melting temperature (° C.) 280 285 285 290 270 280 280 Resin2 NF3040 NF3040 NF3040 — T814 NF3040 + NF3040 + T814 T814 (50/50)(12.5/87.5) Melting temperature 280 285 285 — 270 280 280 (° C.) Layerratio 50/50 50/50 50/50 — 50/50 50/50 50/50 Laminate portion 280 280 280280 270 270 270 temperature (° C.) Adding amount of layerd 4 4 4 4 0 20.5 compound (%) Content of inorganic material 2.6 2.6 2.6 2.6 0.35 1.50.6 (%) Number of layers 100 or more 100 or more 60 1 100 or more 100 ormore 1 MD Preheating temperature (° C.) 45 45 40 — 60 60 45 strechingStreching temperature (° C.) 85 80 80 — 60 60 60 Ratio (times) 3.2 3.23.2 2 3.0 2.0 3.0 Deformation speed (%/min) 4500 4500 4500 — 4300 43004500 Ny(A)-Ny(B) 0.003 0.003 0.003 — 0.008 0.003 0.003 TD Preheatingtemperature (° C.) 110 110 80 — 110 110 60 streching Strechingtemperature (° C.) 130 135 100 — 130 130 110 Ratio (times) 3.8 3.8 3.5 24.0 2.5 4.0 Thermal Temperature (° C.) 210 210 210 — 210 210 210fixation Relaxation Temperature (° C.) 210 210 210 — 210 210 210Relaxation ratio (%) 5 5 5 — 3 3 5 Properties Thickness (μm) 18 20 15 1515 18 19 The in-plane orientation state of ◯ ◯ ◯ X — X ◯ layeredcompound Haze (%) 12.1 12.0 8.2 5.2 1.8 8 23 MD elastic modulus (GPa)2.5 2.5 2.5 0.8 1.5 2.4 1.5 Surface roughness (Sa) 0.0140 0.0130 0.01300.0050 0.1200 0.0210 0.1300 Static friction coefficient μs 0.68 0.650.66 1.8 0.8 0.93 0.79 The number of pinholes 2 2 4 5 2 6 1 In-planeorientation of layered 0.81 0.82 0.49 0.1 or less — 0.7 0.64 compoundEquilibrium moisture content (%) 3.3 3.5 4.5 5.0 2.6 3.8 2.9 Maximumpoint stress × Elongation 18595 20765 27294 13724 13546 13565 15543 at40% RH (X1, MPa* %) Maximum point stress × Elongation 19686 23601 3520922233 32230 26451 35594 at 80% RH (X2, MPa* %) X2/X1 1.06 1.14 1.29 1.622.38 1.95 2.29 In-plane orientation (ΔP) 0.0060 0.0061 0.0062 0.0030.0061 0.0055 0.0059 T814: Polyamide resin produced by Toyobo Co., Ltd.:RV = 2.5, silica content 3500 ppm

Next, the second invention will be described with reference to Examplesand Comparative Examples.

Example 22

After pellets of nylon 6 resin (T-814, produced by Toyobo Co., Ltd.:relative viscosity RV=2.8, containing a lubricant) were vacuum-driedovernight at 100° C., the same resin pellets were supplied to twoextruders and melted at 270° C. and the same kind of resin was laminatedby a static mixer having 10 elements. The laminate was extruded in asheet-like form out of a T die to cooling rolls adjusted at 20° C. andthen cooled and hardened to obtain an un-stretched multilayer sheet. Theratio of the discharge amounts of the two extruders was controlled to be1:1. The thickness of the un-stretched sheet was 250 μm, and thethickness of each layer measured in a cross section was about 1 μm. TheTg of the sheet was 35° C., and the melting point was 225° C. The sheetwas at first preheated at 40° C., stretched 3.2 times by lengthwisestretching at a stretching temperature of 60° C. Next, the sheet wascontinuously led to a tenter and stretched 3.8 times by transversestretching at a preheating temperature of 60° C. and a stretchingtemperature of 130° C. and subjected to thermal fixation at 210° C. and5% transverse relaxation treatment. Thereafter, the film was cooled, andboth rim parts were cut and removed to obtain a biaxially stretchedpolyamide resin film with a thickness of 14 μm. The film had a width of40 cm and a length of 1000 m and was rolled around a paper tube. Thephysical properties at that time are shown in Table 8.

Examples 23 to 31 and Comparative Examples 19 to 26

In Examples 24 and 25, un-stretched sheets with an 8-layer structurewere produced by using a feed block with an 8-layer structure. InComparative Examples 19 to 20, 23, and 25 to 26, un-stretched sheetswith a monolayer structure were produced by using a feed block with amonolayer structure. In Comparative Example 21, an un-stretched sheetwith a 16-layer structure was produced. In Examples 23, 24, 25, 26, and27 and Comparative Example 23, samples were produced under theconditions described in Table 8 and in the same manner as Example 22,except TD stretching was carried out after two-step MD stretching. Thefilm properties are shown in Table 8 for Examples 23 and 24, in Table 9for Examples 25 to 31, in Table 8 for Comparative Examples 19 to 23, andin Table 10 for Comparative Examples 24 to 26.

Comparative Example 27

Pellets of nylon 6 resin containing montmorillonite as a layeredcompound dispersed evenly therein (NF 3040, produced by NanopolymerComposite Corp.; addition amount of the layered compound: 4%) werevacuum-dried overnight at 100° C. Film formation was carried out using amonolayer inflation film formation apparatus. The pellets were suppliedto an extruder and melted at 280° C. Next, the film was extruded out ofa circular die heated at 280° C. and cooled with air and simultaneously,the discharge amount, rolling speed, and tube diameter were adjusted soas to control the stretching ratio of 4 times on the basis of the area.The center part of the tube was cut to obtain a biaxially stretchedpolyamide resin film with a thickness of 25 μm. The physical propertiesat that time are shown in Table 10.

Example 32

Pellets of nylon 6 resin (T-814, produced by Toyobo Co., Ltd.: relativeviscosity RV=28, containing a lubricant), pellets of nylon 6 resincontaining montmorillonite as a layered compound dispersed evenlytherein (NF 3040, produced by Nanopolymer Composite Corp.; additionamount of the layered compound: 4%), and pellets of MXD6 type nylonresin copolymerized with m-xylylenediamine and excellent in the barrierproperty were vacuum-dried overnight at 100° C. A static mixer with 16elements heated at 275° C. was introduced into a melt line between anextruder at the skin layer side and a feed block of a film formationapparatus capable of laminating two-kind three-layers, the pellets ofT814 and NF3040 blended by dry blend at a ratio of 50/50 were suppliedto two extruders at the skin layer side and S6001 was supplied to anextruder at the core layer side. The resins at the skin layer side weremelted at 270° C., the resin at the core layer side was melted at 280°C., and a structure (multilayer structure) in which a monolayer sheetwas sandwiched by two sheets with multilayer structure was formed by afeed block heated at 275° C. The resulting laminate was extruded in asheet-like form out of a T die to cooling rolls adjusted at 20° C. andthen cooled and hardened to obtain an un-stretched multilayer sheet. Theratio of the discharge amounts of the three extruders was controlled tobe 45:10:45. The thickness of the un-stretched sheet was 250 μm, and thethickness of each layer at the skin layer side measured in a crosssection was about 1 μm. The sheet was at first preheated at 70° C.,stretched 3.2 times by lengthwise stretching at a stretching temperatureof 80° C. and a deformation speed of 4500%/min. Next, the sheet wascontinuously led to a tenter and stretched 3.8 times by transversestretching at a preheating 110° C. and thereafter at 135° C. andsubjected to thermal fixation at 210° C. and 5% transverse relaxationtreatment. Thereafter, the film was cooled, and both rim parts were cutand removed to obtain a biaxially stretched polyamide resin film with athickness of 15 μm. The film had a width of 40 cm and a length of 1000 mand was rolled around a paper tube. The physical properties at that timeare shown in Table 10.

TABLE 8 Examples Comparative Examples 22 23 24 19 20 21 22 23 Cast Resin1 T814 T814 T814 T814 T814 T814 T814 T814 Melting temperature (° C.) 270270 270 270 270 270 270 270 Resin 2 T814 T814 S6001 — — — NF3040 —Melting temperature (° C.) 270 270 285 — — — 275 — Layer ratio 50/5050/50 90/10 — — — 75/25 — Laminate portion temperature 270 270 270 270270 270 270 270 (° C.) Adding amount of layerd 0 0 0 0 0 0 1 0 compound(%) Content of inorganic material 0.35 0.35 0.32 0.35 0.35 0.35 1.350.35 (%) Number of layers 100 or more 100 or more 8 1 1 16 100 or more 1MD Preheating temperature (° C.) 40 45 45 40 40 40 40 45 strechingStreching temperature (° C.) 60 60 60 60 60 80 70 60 Ratio (times) 3.22.0, 2.0 2.0, 2.0 2 5.5 2 3 1.75, 1.75 Deformation speed (%/min) 90004500, 4500 4500, 4500 4500 4500 4500 4500 1900, 1900 Ny(A)-Ny(B) 0.00650.0062 0.0062 0.006 0.008 0.004 0.006 0.004 TD Preheating temperature (°C.) 60 60 60 60 60 60 60 60 streching Streching temperature (° C.) 130130 130 130 130 130 130 130 Ratio (times) 8.8 4 4 2 2.5 5 3.5 4 ThermalTemperature (° C.) 210 210 210 210 210 210 210 210 fixation RelaxationTemperature (° C.) 210 210 210 210 210 210 210 210 Relaxation ratio (%)5 3 5 5 5 5 5 5 Properties Thickness (μm) 14 15 15 18 16 15 15 14 Thein-plane orientation state — — — — — — ◯ — of layered compound Haze (%)3 3 3.1 3 3 4 5 2 MD elastic modulus (GPa) 1.5 1.6 1.8 1.2 1.3 1.5 1.91.4 Surface roughness (Sa) 0.12 0.10 0.10 0.11 0.12 0.12 0.09 0.12Static friction coefficient μs 0.8 0.9 1.1 0.8 0.7 0.8 0.75 0.8 Thenumber of pinholes 2 1 4 1 2 2 2 2 In-plane orientation of layered — — —— — — 0.52 — compound In-plane orientation (ΔP) 0.063 0.064 0.062 0.040.06 0.051 0.062 0.063 Boiling strain (%) 0.7 0.4 0.9 0.4 2.8 2.5 2.92.2 Heat shrinkage ratio (%) 1.2 1.3 1.2 1.5 1.6 1.9 1.0 2OTR(cc/m²/day/atm) 22 22 12 22 22 22 18 22 T800: Polyamide resinproduced by Toyobo Co., Ltd.: RV = 2.5, containing no lubricant T814:Polyamide resin produced by Toyobo Co., Ltd.: RV = 2.5, silica content3500 ppm

TABLE 9 Examples 25 26 27 28 29 30 31 Cast Resin 1 NF3040 NF3040 NF3040NF3040 NF3040 NF3040 + NF3040 T814 (50/50) Melting temperature (° C.)280 280 280 280 280 280 280 Resin 2 NF3040 NF3040 NF3040 NF3040 NF3040NF3040 + NF3040 T814 (50/50) Melting temperature (° C.) 280 280 280 280280 280 280 Layer ratio 50/50 55/45 50/50 50/50 50/50 50/50 50/50Laminate portion temperature 285 280 285 300 310 290 310 (° C.) Addingamount of layerd 4 4 4 4 4 2 4 compound (%) Content of inorganicmaterial (%) 2.6 2.6 2.6 2.6 2.6 1.5 2.6 Number of layers 8 100 or more100 or more 100 or more 100 or more 100 or more 100 or more MDPreheating temperature (° C.) 45 45 45 45 45 45 45 streching Strechingtemperature (° C.) 80 80 80 85 85 80 80 Ratio (times) 2.0 × 2.0 1.5 ×2.3 2.3 × 1.5 3.2 3.2 3.2 2.0 × 2.0 Deformation speed (%/min) 1950 +1950 1200 + 2700 2700 + 1200 4500 4500 4500 1950 + 1950 Ny(A)-Ny(B)0.004 0.002 0.004 0.003 0.003 0.003 0.003 TD Preheating temperature (°C.) 110 110 110 110 110 100 110 streching Streching temperature (° C.)135 135 135 130 130 125 130 Ratio (times) 3 4 4 3.8 3.8 3.8 4.5 ThermalTemperature (° C.) 210 210 210 215 210 210 210 fixation RelaxationTemperature (° C.) 210 210 210 210 210 210 210 Relaxation ratio (%) 5 55 5 5 5 3 Properties Thickness (μm) 15 13 14 18 18 15 14 The in-planeorientation state of ◯ ◯ ◯ ◯ ◯ ◯ ◯ layered compound Haze (%) 10 10 11 1414 8 6.5 In-plane orientation (ΔP) 0.059 0.061 0.064 0.061 0.06 0.0650.064 MD elastic modulus (GPa) 2.4 1.9 1.9 2.5 2.5 2 2.7 Surfaceroughness (Sa) 0.025 0.024 0.024 0.0128 0.0128 0.015 0.015 Staticfriction coefficient μs 0.82 0.8 0.8 0.79 0.79 0.94 0.8 The number ofpinholes 2 1 1 3 3 6 1 In-plane orientation of layered 0.55 0.81 0.840.8 0.82 0.74 0.88 compound Boiling strain (%) 0.9 0.7 1.3 1.7 1.4 0.90.6 Heat shrinkage ratio (%) 1.3 1.2 0.9 0.1 0.2 0.8 0.3OTR(cc/m²/day/atm) 11 12 10 11 10.5 14.5 14

TABLE 10 Comparative Examples Example 24 25 26 27 32 Cast Resin 1 (skinlayer side) NF3040 NF3040 NF3040 + NF3040 NF3040 + T814 (50/50) T814(50/50) Melting temperature (° C.) 280 280 280 280 270 Resin 2 (skinlayer side) NF3040 — — — NF3040 + T814 (50/50) Melting temperature (°C.) 260 — — — 270 Resin 3(core layer side) — — — — S6001 Meltingtemperature (° C.) — — — — 280 Layer ratio 50/0/50 — — — 45/10/45Laminate portion temperature of resin 285 280 285 280 275 1 and resin 2(° C.) Laminate portion temperature of — — — — 275 resins 1-3 (° C.)Adding amount of layerd compound 4 4 2 4 1.8 (%) Content of inorganicmaterial (%) 2.6 2.6 1.5 2.6 1.3 Number of layers 100 or more 1 1 1 100or more MD Preheating temperature (° C.) 45 45 45 — 70 strechingStreching temperature (° C.) 85 85 80 — 80 Ratio (times) 4 3 3 2 3.2Deformation speed (%/min) 4800 4500 500 — 4500 Ny(A)-Ny(B) 0.001 0.0000.000 — 0.003 TD Preheating temperature (° C.) 110 110 110 — 110streching Streching temperature (° C.) 135 135 135 — 135 Ratio (times) 22 3.5 2 3.8 Thermal Temperature (° C.) 210 210 210 — 210 fixationRelaxation Temperature (° C.) 210 210 210 — 210 Relaxation ratio (%) 5 55 — 5 Properties Thickness (μm) 18 20 18 25 15 The in-plane orientationstate X X ◯ X of layered compound Haze (%) 10 25 40 3 7 MD elasticmodulus (GPa) 0.9 0.9 2.2 0.7 2.6 Surface roughness (Sa) 0.15 0.14 0.0140.005 0.18 Static friction coefficient μs 1.1 1.12 0.78 1.8 0.45 Thenumber of pinholes 25 35 14 5 2 In-plane orientation of layered 0.2 0.10.45 0.1 or less 0.66 compound In-plane orientation (ΔP) 0.0062 0.0550.056 0.056 0.006 Boiling strain (%) 3.4 2.2 3.4 2 1.6 Heat shrinkageratio (%) 2.1 2.5 3.3 1.0 1.0 OTR(cc/m²/day/atm) 30 15 25 2.0 10

INDUSTRIAL APPLICABILITY

A conventional nylon film is made easy to slip by roughing the surfacein the case the slipping property under high humidity is requiredbecause the slipping property fluctuates in accordance with thehumidity. However, according to the first invention, since a filmcontaining an inorganic layered compound has little effect on theslipping property relative to the humidity level and sufficient slippingis observed even if the surface roughness is small, contradictorycharacteristics such as slip and gloss can be simultaneously satisfied.The layered compound is in-plane orientated to a high level, so that theeffect of improving various characteristics can be extracted to theultimate extent, such that the film is excellent in appearance, has highproductivity, and high industrial value. Further, the obtained film hasan excellent oxygen barrier property, dimensional stability, mechanicalcharacteristics, and piercing strength. Thus, it is possible to producea film having improved mechanical characteristics in low humidity andlowered humidity dependence of the impact strength at a low speed with ahigh productivity, so that the film can be used in applications, forwhich conventional films were previously difficult to use. Thus, thefilms described herein are useful as industrial materials other thanwrapping materials for food, drug, and general goods.

Further, a conventional biaxially stretched polyamide resin film showssignificant boiling strain due to bowing of the film if the in-planeorientation is increased for improving the mechanical characteristics.In the case of the biaxially stretched multilayer polyamide resin filmof the second invention, the boiling strain in the end parts in the filmwidth direction is diminished by lowering the stretching stress, andproductivity of films with low boiling strain can be improved.Furthermore, addition of the layered compound to each layer makes itpossible to produce a film excellent in not only the boiling strain butalso the mechanical characteristics and the barrier property.

The invention claimed is:
 1. A biaxially stretched polyamide resin filmcontaining 0.3 to 10 wt. % of an inorganic material including a layeredcompound and having a laminate structure of 8 or more layers in total,wherein the layered compound is in-plane oriented and the film has ahaze of 1.0 to 20%, an elastic modulus in the longitudinal direction of1.7 to 3.5 GPa at a relative humidity of 35% RH, a surface roughness(Sa) of 0.01 to 0.1 μm, and a static friction coefficient (F/B) of 0.3to 1.0 at a normal stress of 0.5 N/cm².
 2. The biaxially stretchedpolyamide resin film as described in claim 1, wherein the number ofpinholes after 1000 times Gelbo Flex test at 23° C. is 0 to
 30. 3. Thebiaxially stretched polyamide resin film as described in claim 2,wherein the film is transversely stretched at a transverse stretchingtemperature of 50 to 155° C.
 4. The biaxially stretched polyamide resinfilm as described in claim 1, wherein the film is transversely stretchedat a transverse stretching temperature of 50 to 155° C.
 5. The biaxiallystretched polyamide resin film as described in claim 1, wherein the filmhas a thickness of 3 to 200 μm, and the in-plane orientation degree ofthe inorganic layered compound measured by x-ray diffractometry is in arange of 0.4 to 1.0.
 6. The biaxially stretched polyamide multilayerresin film as described in claim 5, wherein a static mixer method isemployed at the time of melt extrusion of a thermoplastic resin and theresin temperature immediately before introduction into the static mixeris in a range from the melting point to melting point +70° C. and theheater temperature in the latter half of the static mixer is set to behigher by 5° C. or more and by 40° C. or less than the resin temperatureimmediately before introduction into the static mixer.
 7. The biaxiallystretched polyamide resin film as described in claim 1, wherein thelayered compound is in-plane oriented and the in-plane orientation (ΔP)of the film is 0.057 to 0.075, and the value of piercingstrength/thickness of the film is 0.88 to 2.50 (N/μm).
 8. The biaxiallystretched polyamide resin film as described in claim 7, wherein thestretching ratio on the basis of an area by biaxial stretching measuredas the product of the stretching ratio in the lengthwise direction andthe stretching ratio in the transverse direction is 8.5 times or more.9. The biaxially stretched polyamide resin film as described in claim 8,wherein biaxial stretching is successive biaxial stretching inlengthwise stretching-transverse stretching order and when Ny is definedas a refractive index in the center part in the width direction of thefilm, the difference Ny(A)−Ny(B) between Ny(A) which is Ny of the sheetbefore lengthwise stretching and Ny(B) which is Ny of the sheet afteruniaxial stretching is 0.003 or higher.
 10. The biaxially stretchedpolyamide resin film as described in claim 7, wherein biaxial stretchingis successive biaxial stretching in lengthwise stretching-transversestretching order and when Ny is defined as a refractive index in thecenter part in the width direction of the film, the differenceNy(A)−Ny(B) between Ny(A) which is Ny of the sheet before lengthwisestretching and Ny(B) which is Ny of the sheet after uniaxial stretchingis 0.003 or higher.
 11. The biaxially stretched polyamide resin film asdescribed in claim 1, wherein the film is obtained by stretching as muchas 2.5 to 5.0 times in the longitudinal direction and 3.0 to 5.0 timesin the width direction, and the film has a ratio of the product (X1) ofthe maximum point stress (MPa) and a breaking elongation (%) of a samplestored at a humidity of 40% for 12 hours and the product (X2) of themaximum point stress (MPa) and a breaking elongation (%) of a samplestored at a relative humidity of 80% for 12 hours is in a range of 1.0to 1.5 when the maximum point stress and breaking elongation is measuredby a method as described in JIS K 7113 under conditions of a startinglength of 40 mm, a width of 10 mm, and a deformation rate of 200 mm/minafter storage at an equilibrium water absorption ratio of 3.0 to 7.0%and a relative humidity of 40%.